access_out: add CAN_SEEK control

Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

include/vlc_sout.h

@@ -81,6 +81,7 @@ struct sout_access_out_t
 enum access_out_query_e
 {
     ACCESS_OUT_CONTROLS_PACE, /* arg1=bool *, can fail (assume true) */
+    ACCESS_OUT_CAN_SEEK, /* arg1=bool *, can fail (assume true) */
 };
 
 VLC_API sout_access_out_t * sout_AccessOutNew( vlc_object_t *, const char *psz_access, const char *psz_name ) VLC_USED;