BUG/MEDIUM: ssl: create the mux immediately on early data

BUG/MEDIUM: ssl: create the mux immediately on early data

If we received early data, and an ALPN has been negociated, then
immediately try to create a mux if we did not have one already.
Generally, at this point we would not have one, as the mux is decided by
the ALPN, however at this point, even if the handshake is not done yet,
we have enough to determine the ALPN, so we can immediately create the
mux.
Doing so makes up able to treat the request immediately, without waiting
for the handshake to be done.

This should be backported up to 2.8.