If `ipfw fwd' loops an mbuf back to ip_input from ip_output and the mbuf is marked for delayed checksums, then additionally mark the packet as having it's checksums computed.  This allows us to bypass computing/checking the checksum entirely, which isn't really needeed as the packet has never hit the wire.
If `ipfw fwd' loops an mbuf back to ip_input from ip_output and the
mbuf is marked for delayed checksums, then additionally mark the
packet as having it's checksums computed.  This allows us to bypass
computing/checking the checksum entirely, which isn't really needeed
as the packet has never hit the wire.

Reviewed by:		green

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