CLEANUP: listener: store stream vs dgram at the bind_conf level

CLEANUP: listener: store stream vs dgram at the bind_conf level

Let's collect the set of xprt-level and sock-level dgram/stream protocols
seen on a bind line and store that in the bind_conf itself while they're
being parsed. This will make it much easier to detect incompatibilities
later than the current approch which consists in scanning all listeners
in post-parsing.