ns2: migrate from osmo_sock_set_dscp() to OSMO_SOCK_F_DSCP()

The latter is much more compact than the former.

Change-Id: I2a24c0cbb17fad8ed84297267dcd63730efbc014
diff --git a/src/gb/gprs_ns2_frgre.c b/src/gb/gprs_ns2_frgre.c
index f888af2..9391343 100644
--- a/src/gb/gprs_ns2_frgre.c
+++ b/src/gb/gprs_ns2_frgre.c
@@ -589,25 +589,16 @@
 	priv->fd.data = bind;
 	priv->addr = *local;
 	INIT_LLIST_HEAD(&bind->nsvc);
+	priv->dscp = dscp;
 
 	rc = osmo_sock_init_osa_ofd(&priv->fd, SOCK_RAW, IPPROTO_GRE,
 				 local, NULL,
-				 OSMO_SOCK_F_BIND);
+				 OSMO_SOCK_F_BIND | OSMO_SOCK_F_DSCP(priv->dscp));
 	if (rc < 0) {
 		gprs_ns2_free_bind(bind);
 		return rc;
 	}
 
-	if (dscp > 0) {
-		priv->dscp = dscp;
-
-		rc = setsockopt(priv->fd.fd, IPPROTO_IP, IP_TOS,
-				&dscp, sizeof(dscp));
-		if (rc < 0)
-			LOGBIND(bind, LOGL_ERROR, "Failed to set the DSCP to %d with ret(%d) errno(%d)\n",
-				dscp, rc, errno);
-	}
-
 	if (result)
 		*result = bind;
 
diff --git a/src/gb/gprs_ns2_udp.c b/src/gb/gprs_ns2_udp.c
index 22d371f..0de207c 100644
--- a/src/gb/gprs_ns2_udp.c
+++ b/src/gb/gprs_ns2_udp.c
@@ -352,24 +352,16 @@
 	priv->fd.cb = nsip_fd_cb;
 	priv->fd.data = bind;
 	priv->addr = *local;
+	priv->dscp = dscp;
 
 	rc = osmo_sock_init_osa_ofd(&priv->fd, SOCK_DGRAM, IPPROTO_UDP,
 				 local, NULL,
-				 OSMO_SOCK_F_BIND);
+				 OSMO_SOCK_F_BIND | OSMO_SOCK_F_DSCP(priv->dscp));
 	if (rc < 0) {
 		gprs_ns2_free_bind(bind);
 		return rc;
 	}
 
-	if (dscp > 0) {
-		priv->dscp = dscp;
-
-		rc = osmo_sock_set_dscp(priv->fd.fd, dscp);
-		if (rc < 0)
-			LOGBIND(bind, LOGL_ERROR, "Failed to set the DSCP to %d with ret(%d) errno(%d)\n",
-				dscp, rc, errno);
-	}
-
 	/* IPv4: max fragmented payload can be (13 bit) * 8 byte => 65535.
 	 * IPv6: max payload can be 65535 (RFC 2460).
 	 * UDP header = 8 byte */