ON-16037: added functions to read stats for interfaces

[rdrinkwa-xilinx]

Added two functions to read the drop stats from the physical interfaces used by TCPDirect. Tested as working with physical interfaces themselves or a bond. The zfsink app was updated to make use of this additional functionality for testing and demo purposes.

The design mimics that of ef_vi itself with the two calls to get the layout and then the actual stats themselves. It could be changed to hold a copy of the layout internally within the stack so passing it back in wouldn't be required but it would add complexity and necessitate code changes in other files beyond the minimal updates to existing files here.

Testing with 'efsend' sending 1000 1-byte packets as a burst that is known to exceed zfsink's ability to avoid drops.

# testing physical interface with regular drops
[server1:static]$ ZF_ATTR="interface=enp1s0f0" ./zfsink -s 224.1.2.3:12345
# pkt-rate  bandwidth(Mbps)       total-pkts  RX CRC errors  RX trunk errors  RX no descriptor errors  RX abort errors
         0                0                0              0                0                        0                0
         0                0                0              0                0                        0                0
       710                0              710              0                0                      290                0
         0                0              710              0                0                        0                0
         0                0              710              0                0                        0                0
^C
# physical interface and backgrounded to cause more drops
[server1:static]$ ZF_ATTR="interface=enp1s0f0" ./zfsink -s 224.1.2.3:12345
# pkt-rate  bandwidth(Mbps)       total-pkts  RX CRC errors  RX trunk errors  RX no descriptor errors  RX abort errors
         0                0                0              0                0                        0                0
^Z
[1]+  Stopped                 ./zfsink -s 224.1.2.3:12345
[server1:static]$ fg
ZF_ATTR="interface=enp1s0f0" ./zfsink -s 224.1.2.3:12345
         0                0                0              0                0                      496                0
       504                0              504              0                0                        0                0
         0                0              504              0                0                        0                0
^C
 # running on a bond with burst on first then second intf. Output changed to show one line per intf.
[server1:static]$ ZF_ATTR="interface=bond0" ./zfsink -s 224.1.2.3:12345
# pkt-rate  bandwidth(Mbps)       total-pkts
#  RX CRC errors RX trunk errors RX no descriptor errors RX abort errors
         0                0                0
              0                0                        0                0
              0                0                        0                0
         0                0                0
              0                0                        0                0
              0                0                        0                0
       744                0              744
              0                0                      256                0
              0                0                        0                0
         0                0              744
              0                0                        0                0
              0                0                        0                0
       760                0             1504
              0                0                        0                0
              0                0                      240                0
         0                0             1504
              0                0                        0                0
              0                0                        0                0
         0                0             1504
              0                0                        0                0
              0                0                        0                0
^C
[server1:static]$

[ligallag-amd]

I think you need to make static method which does the following.

pthread_mutex_lock(&printf_mutex);
printf(...)
pthread_mutex_unlock(&printf_mutex);

There is too much duplicated code. Please update #50 to do this also.