mtp: Rename mtp_link to mtp_link_set as this is the linkset

The link_udp is actually below the linkset. We need to get this
right now and then can have multiple links.
diff --git a/src/link_udp.c b/src/link_udp.c
index 7fcf6f1..e5e476c 100644
--- a/src/link_udp.c
+++ b/src/link_udp.c
@@ -113,7 +113,7 @@
 	LOGP(DINP, LOGL_DEBUG, "MSU data on: %p data %s.\n", link, hexdump(msg->data, msg->len));
 	if (link->pcap_fd >= 0)
 		mtp_pcap_write_msu(link->pcap_fd, msg->l2h, msgb_l2len(msg));
-	mtp_link_data(link->the_link, msg);
+	mtp_link_set_data(link->the_link, msg);
 
 exit:
 	msgb_free(msg);