extcap: fix memory leak

found by valgrind

Change-Id: I8c5226a08be797ce72ec937138a6681d946fb13c
Reviewed-on: https://code.wireshark.org/review/20720
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Roland Knall <rknall@gmail.com>

extcap.c

@@ -1388,7 +1388,7 @@ static void remove_extcap_entry(gpointer entry, gpointer data _U_)
     extcap_interface *int_iter = (extcap_interface*)entry;
 
     if (int_iter->if_type == EXTCAP_SENTENCE_EXTCAP)
-        g_free(int_iter);
+        extcap_free_interface(entry);
 }
 
 static gboolean cb_load_interfaces(extcap_callback_info_t cb_info)