udscs: simplify traffic logging

Remove @type_to_string, @no_types arguments from
udscs_connect(), udscs_create_server{,_for_fd}().
udscs is used only in vdagent.c and vdagentd.c
and in both cases the args are the same
(vdagentd_messages, VDAGENTD_NO_MESSAGES).

Add debug_print_message_header().

Signed-off-by: Jakub Janků <jjanku@redhat.com>
Acked-by: Victor Toso <victortoso@redhat.com>