net/frr9: Update to 9.1.2

The RC script was almost completely rewritten to align with upstream and match
the new defaults:

• Use integrated mode (only one configuration file);
• Use watchfrr, which is responsible for starting, monitoring, and stopping daemons;
• Use the upstream recommended flags for all daemons (vty bound to localhost).

ChangeLog: https://github.com/FRRouting/frr/releases/tag/frr-9.1.2
Reported by: portscout