[nat] Add ip-tos option to the nat.

This is applied to all incoming BSC connections.
diff --git a/openbsc/src/nat/bsc_nat.c b/openbsc/src/nat/bsc_nat.c
index 3b3bf69..53b8882 100644
--- a/openbsc/src/nat/bsc_nat.c
+++ b/openbsc/src/nat/bsc_nat.c
@@ -872,6 +872,11 @@
 	if (rc != 0)
                 LOGP(DNAT, LOGL_ERROR, "Failed to set TCP_NODELAY: %s\n", strerror(errno));
 
+	rc = setsockopt(fd, IPPROTO_IP, IP_TOS,
+			&nat->bsc_ip_tos, sizeof(nat->bsc_ip_tos));
+	if (rc != 0)
+		LOGP(DNAT, LOGL_ERROR, "Failed to set IP_TOS: %s\n", strerror(errno));
+
 	/* todo... do something with the connection */
 	/* todo... use GNUtls to see if we want to trust this as a BTS */