gtp: Add support for checking GTP device type

Add a function that checks if a net device type is GTP.

Signed-off-by: Wojciech Drewek <wojciech.drewek@intel.com>
Reviewed-by: Harald Welte <laforge@gnumonks.org>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

include/net/gtp.h

@@ -63,6 +63,12 @@ struct gtp_pdu_session_info {	/* According to 3GPP TS 38.415. */
 	u8	qfi;
 };
 
+static inline bool netif_is_gtp(const struct net_device *dev)
+{
+	return dev->rtnl_link_ops &&
+		!strcmp(dev->rtnl_link_ops->kind, "gtp");
+}
+
 #define GTP1_F_NPDU	0x01
 #define GTP1_F_SEQ	0x02
 #define GTP1_F_EXTHDR	0x04