OPNsense 24.7 - support unicast CARP announcements #7486

Important notices

Before you add a new report, we ask you kindly to acknowledge the following:

• I have read the contributing guide lines at https://github.com/opnsense/core/blob/master/CONTRIBUTING.md
• I am convinced that my issue is new after having checked both open and closed issues at https://github.com/opnsense/core/issues?q=is%3Aissue

Is your feature request related to a problem? Please describe.

FreeBSD 14.x support unicast carp announcements, which would be practical to offer in our gui as well.

Describe the solution you like

Add optional peer and peer6 values in Interfaces: Virtual IPs: Settings for carp type interfaces.

Describe alternatives you considered

none

Additional context

https://man.freebsd.org/cgi/man.cgi?carp

• add a note in the docs about source selection (https://github.com/opnsense/src/blob/dc96e48a8d362b6db096560cf93cce98fa7fc25c/sys/netinet/ip_carp.c#L923-L924), ifa_preferred() seems just to select the first address which might be problematic when using unicast