net/frr8: remove vtysh port option, housekeeping, fix build with SNMP

Remove the vtysh port option due to upstream breakage. At this time, both
net/frr8 and net/frr9 cannot be built without vtysh. This is an uncommon
scenario and upstream does not currently test this build option.
Also cleanup the Makefile and pkg-plist structure and ordering.

PR: 272757
Reported by: R. Christian McDonald <rcm@rcm.sh>, brd
Obtained from: R. Christian McDonald <rcm@rcm.sh>