xshared: Print protocol numbers if --numeric was given

xshared: Print protocol numbers if --numeric was given

This is much trickier than expected: On one hand, proto_to_name() is
used to lookup protocol extensions so must resolve despite FMT_NUMERIC
being set. On the other, --verbose implies --numeric but changing the
output there is probably a bad idea. Luckily the latter situation is
identified by FMT_NOTABLE bit.

Signed-off-by: Phil Sutter <phil@nwl.cc>