crimson/mon: resend mon command when session established

crimson/mon: resend mon command when session established

this behavior matches that of `MonClient::_resend_mon_commands()`. so
far the only user which sends mon command in crimson is
`OSD::_add_me_to_crush()`, but there is still (rare) chance that the connected
monitor cannot be reached when we send the command to it, in that case,
we should retry when the connection is re-established.

Signed-off-by: Kefu Chai <kchai@redhat.com>