msg: make loopback Connection feature accurate all the time

msg: make loopback Connection feature accurate all the time

In 626360aab05545ddacb0ac28e54a70e31fd5695d we made the
OSD cluster loopback connection CEPH_FEATURES_ALL, but
all other loopback connections got features == 0.  I
can't come up with any reason we wouldn't want those
connections to have accurate feature bits, so let's just
use CEPH_FEATURES_ALL for all of them.

While we're here, make the cflags argument required.

Signed-off-by: Sage Weil <sage@redhat.com>