[DHCP] Fix RFC4390 client identifier constructions.

RFC 4390 provides for the DHCP client identifier to contain the link-layer
hardware type and MAC address when the MAC address exceeds 16 bytes.
However, the hardware type field is only 8 bits; we were assuming 16 bits.

src/net/udp/dhcp.c

 	/* Add DHCP client identifier.  Required for Infiniband, and
 	 * doesn't hurt other link layers.
 	 */
-	client_id.ll_proto = netdev->ll_protocol->ll_proto;
+	client_id.ll_proto = ntohs ( netdev->ll_protocol->ll_proto );
 	ll_addr_len = netdev->ll_protocol->ll_addr_len;
 	assert ( ll_addr_len <= sizeof ( client_id.ll_addr ) );
 	memcpy ( client_id.ll_addr, netdev->ll_addr, ll_addr_len );