Support for 24 Art-Net universes

[SpComb]

Fix artnet input to use an eventgroup instead of problematic top-level task notifications.

Use separate dmx/sync event bits instead of the sync_mode bit in struct artnet_dmx. Change leds artnet logic to bypass soft-sync when in artnet sync mode.

Split per-output event bits into a separate event group, increasing the maximum artnet output count from 20 -> 24.

Tweak the ETH DMA buffer size/num to take into consideration the actual DMA buffer usage for expected Art-Net frame sizes vs maximum Ethernet frame size. This optimizes the fixed memory usage for DMA buffers by approx 15KB while increasing the number of Art-Net frames in the DMA buffer from 24 to 32, at the cost of each maximum-sized ethernet frame using two DMA buffers instead of one.

Bump both CONFIG_LWIP_UDP_RECVMBOX_SIZE and CONFIG_LWIP_TCPIP_RECVMBOX_SIZE to handle bursts of up to 32 packets.

[SpComb]

Tend to see one artnet_send_poll_reply -> artnet_send: send: Not enough space at boot, and the first batch of ArtPollReply is missing some packets, but it works fine after that.

Not sure why, it's only 24/4 -> 6 packet burst, and should fit into CONFIG_ETH_DMA_TX_BUFFER_NUM=10 . Perhaps something else is filling up the TX queue at boot.

EDIT: confirm that the ArtPollReply is only 281 bytes including the Ethernet framing, and the 6-packet burst should easily fit into CONFIG_ETH_DMA_TX_BUFFER_NUM=10.