netmap: bridge: fix NS_MOREFRAG support

Support for NS_MOREFRAG is broken, as NS_MOREFRAG is copied from
the TX slot to the RX slot rather than the other way around.
Also, the NS_MOREFRAG must be copied also in case of packet
copy (no zerocopy).

Reported by: rajesh1.kumar_amd.com
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D27980