BK SDK boards with CFG_LWIP_MEM_POLICY=LWIP_REDUCE_THE_PLAN (e.g. CB3S/
BK7231N) set PBUF_POOL_SIZE=3, which is too small for TCP_WND=4*MSS:
3*(1580-54)=4578 < 5840. Set PBUF_POOL_SIZE=4 on BK72XX so the lwIP
compile-time sanity check passes: 4*1526=6104 > 5840.
RTL(20) and LN(20) already have large enough PBUF pools.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>