mgr/cephadm: select IPs/interface based on VIP for keepalive conf

mgr/cephadm: select IPs/interface based on VIP for keepalive conf

We need to make sure the keepalive conf sets
the unicast src and peer IPs to be the ones
in the same subnet as the VIP we're setting up,
as well as specify the correct interface. Otherwise,
the keepalive daemons don't speak to each other
properly and all end up going into MASTER state.

Fixes: https://tracker.ceph.com/issues/62276
Signed-off-by: Adam King <adking@redhat.com>
(cherry picked from commit 58ddc4e20f7cead1f2594241450f4beb5230c746)

Conflicts:
	src/pybind/mgr/cephadm/tests/test_services.py