Add comment about udp checksums being off in BSD 4.2 compatibility mode.
Add comment about udp checksums being off in BSD 4.2 compatibility mode.

Submitted by: Dr. Markus Waldeck
PR: kern/106657

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase