MINOR: mux-quic: properly set the flags and name fields

MINOR: mux-quic: properly set the flags and name fields

The mux didn't have its flags nor name set, as seen in this output of
"haproxy -vv":

 Available multiplexer protocols :
 (protocols marked as <default> cannot be specified using 'proto' keyword)
   quic : mode=HTTP  side=FE     mux=      flags=
     h2 : mode=HTTP  side=FE|BE  mux=H2    flags=HTX|CLEAN_ABRT|HOL_RISK|NO_UPG

This might have random impacts at certain points like forcing some
connections to close instead of aborting a stream, or not always
handling certain streams as fully HTX-compliant.