net/frr9: Install daemons in lib/frr, fix SNMP build and rc.d restart

Daemons move from ${PREFIX}/sbin to ${PREFIX}/lib/frr, matching the Linux
packages and net/frr10. Only vtysh and frr-reload stay in bin/ and sbin/.
This avoids filename collision with net/openbgpd*, net/pimd, net/quagga, etc.

Fix the SNMP build.

Backport frr10's rc.d fixes: a bare "service frr restart" restarted watchfrr
only, leaving the daemons it supervises untouched.