tshark: register extcap preferences

Bug: 12949
Change-Id: I95ef8a15a2d629bbb351d34dbfc730fa5ea62cd5
Reviewed-on: https://code.wireshark.org/review/17954
Petri-Dish: Pascal Quantin <pascal.quantin@gmail.com>
Reviewed-by: Roland Knall <rknall@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>

tshark.c

@@ -813,6 +813,9 @@ main(int argc, char *argv[])
      by stats_tree_stat.c and need to registered before that */
 #ifdef HAVE_PLUGINS
   register_all_plugin_tap_listeners();
+#endif
+#ifdef HAVE_EXTCAP
+    extcap_register_preferences();
 #endif
   register_all_tap_listeners();
   conversation_table_set_gui_info(init_iousers);