bsdsocket: drain parked closes past transient holds (#53)

[tinic]

Fixes #70

Steps 2 and 3 of #70: the scanner is a CI gate, and the remaining test sites are fixed.

Gate. tools/check-lvo-clobbers.sh runs tools/check-lvo-clobbers.py over src/ and tests/. It flags every extended asm statement that calls through a6 and does not list d0, d1, a0 and a1 as outputs or clobbers. It reads register declarations through object-like macros (BSD_SCRATCH, NETDEV_REG_A1) from the file and from its "..." includes, and it skips top-level asm. Output is key=value, and the exit code is 1 on any flagged site. The gate runs in stage_host next to check-lvo-matrix.sh, is registered in check-gates-wired.sh, and is on the shellcheck list.

Validation

tree	statements	flagged
58c5c4f (the tree the issue scanned)	415	31
main 7fa3df3 (before)	415	14
this branch (after)	415	0
src/tools/toolsock.c alone	22	0

• On 58c5c4f, all 16 shipped sites are flagged with exactly the missing sets the issue lists, and tests/sockopt/sockopt_test.c:332 (pre-sockopt_test: the recvfrom helper declares a1 clobbered #68) is flagged missing=a1.
• The issue's 77 included 46 false positives:
  • 43 BSD_SCRATCH macro sites in ipv6_socket_test, sockopt_test and udpdrill
  • apidrill's TH() macro, which lists all eight registers
  • the top-level asm in genet.c:542 and netdev_cache.c:85

Fixes (14 test sites). A missing register that is also an input becomes an output: a dummy "=r", or "+r" as in #71. A missing register that is not an input becomes a clobber.

• atf_main:64 (a0, d0)
• tickprobe:120 (d1)
• endurance:118 (d1)
• ipv6_socket_test:667 (d0)
• refused_leak_test:98 (d1)
• tcpdrill:156 and :266 (d1)
• tls_loop:270 (d1)
• cardgrab:66 and :80 (a1)
• ifprobe:829 and :844 (a0)
• udpdrill:195 and :277 (a1). These are the sockopt_test: the recvfrom helper declares a1 clobbered #68 recvfrom/getsockopt shape.

Repro: tools/check-lvo-clobbers.sh; echo $?

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