slirp: fix guestfwd id

When using -net user,guestfwd=... Qemu immediately complains about the id
being in invalid format. This is because we pass in an id that contains a
colon, while the id restrictions don't allow colons.

This patch changes the colon into a dot, making guestfwd work again.
Signed-off-by: NAlexander Graf <agraf@suse.de>
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>

net/slirp.c

@@ -614,7 +614,7 @@ static int slirp_guestfwd(SlirpState *s, const char *config_str,
     }
 
     fwd = qemu_malloc(sizeof(struct GuestFwd));
-    snprintf(buf, sizeof(buf), "guestfwd.tcp:%d", port);
+    snprintf(buf, sizeof(buf), "guestfwd.tcp.%d", port);
     fwd->hd = qemu_chr_open(buf, p, NULL);
     if (!fwd->hd) {
         error_report("could not open guest forwarding device '%s'", buf);