It seems all Broadcom controllers have a bug that can generate UDP

It seems all Broadcom controllers have a bug that can generate UDP
datagrams with checksum value 0 when TX UDP checksum offloading is
enabled.  Generating UDP checksum value 0 is RFC 768 violation.
Even though the probability of generating such UDP datagrams is
low, I don't want to see FreeBSD boxes to inject such datagrams
into network so disable UDP checksum offloading by default.  Users
still override this behavior by setting a sysctl variable or loader
tunable, dev.bge.%d.forced_udpcsum.

I have no idea why this issue was not reported so far given that
bge(4) is one of the most commonly used controller on high-end
server class systems. Thanks to andre@ who passed the PR to me.

PR:	kern/104826