cephadm: Split multicast interface and unicast_ip in keepalived.conf

cephadm: Split multicast interface and unicast_ip in keepalived.conf

When deploying keepalived, cephadm set interface and unicast_src_ip
in keepalived.conf. However, having both options are set, but
if unicast_src_ip is not in the interface set by 'interface',
the instrances of keepalived will not properly commuicate.

This commit makes both options exclusive, and add an option to set
either one or the other. Default is set to 'interface', as it seems
multicast is the default way to deploy keepalived.

Signed-off-by: Luis Domingues <domingues.luis@protonmail.ch>
(cherry picked from commit 0dfe3e68a9284736f643a06acfda719cec0a6ea4)
(cherry picked from commit 837c273da2aa3dd3b3fe09b9ac04fd032149de6d)