tree-wide: use coccinelle to patch a lot of code to use mfree()

This replaces this:

        free(p);
        p = NULL;

by this:

        p = mfree(p);

Change generated using coccinelle. Semantic patch is added to the
sources.

src/core/socket.c

@@ -135,11 +135,8 @@ static void socket_done(Unit *u) {
 
         unit_ref_unset(&s->service);
 
-        free(s->tcp_congestion);
-        s->tcp_congestion = NULL;
-
-        free(s->bind_to_device);
-        s->bind_to_device = NULL;
+        s->tcp_congestion = mfree(s->tcp_congestion);
+        s->bind_to_device = mfree(s->bind_to_device);
 
         free(s->smack);
         free(s->smack_ip_in);