eth: fbnic: increase FBNIC_HDR_BYTES_MIN from 128 to 256 bytes

eth: fbnic: increase FBNIC_HDR_BYTES_MIN from 128 to 256 bytes

Increase FBNIC_HDR_BYTES_MIN from 128 to 256 bytes. The previous minimum
was too small to guarantee that very long L2+L3+L4 headers always fit
within the header buffer. When EN_HDR_SPLIT is disabled and a packet
exceeds MAX_HEADER_BYTES, splitting occurs at that byte offset instead
of the header boundary, resulting in some of the header landing in the
payload page. The increased minimum ensures headers always fit with the
MAX_HEADER_BYTES cut off and land in the header page.

Fixes: 2b30fc01a6c7 ("eth: fbnic: Add support for HDS configuration")
Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
Acked-by: Mohsin Bashir <mohsin.bashr@gmail.com>
Link: https://patch.msgid.link/20260211-fbnic-tcp-hds-fixes-v1-2-55d050e6f606@meta.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>