MINOR: tcp_act: remove limitation on protocol for attach-srv

MINOR: tcp_act: remove limitation on protocol for attach-srv

This patch allows to specify "tcp-request session attach-srv" without
requiring that each associated bind lines mandates HTTP/2 usage. If a
non supported protocol is targetted by this rule, conn_install_mux_fe()
is responsible to reject it.

This change is mandatory to be able to mix attach-srv and standard
non-reversable connection on the same bind instances. An ACL can be used
to activate attach-srv only on some conditions.