tcp: add OFO snmp counters

Add three SNMP TCP counters, to better track TCP behavior
at global stage (netstat -s), when packets are received
Out Of Order (OFO)

TCPOFOQueue : Number of packets queued in OFO queue

TCPOFODrop  : Number of packets meant to be queued in OFO
              but dropped because socket rcvbuf limit hit.

TCPOFOMerge : Number of packets in OFO that were merged with
              other packets.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/snmp.h b/include/linux/snmp.h
index 2e68f5b..6e4c511 100644
--- a/include/linux/snmp.h
+++ b/include/linux/snmp.h
@@ -233,7 +233,10 @@
 	LINUX_MIB_TCPREQQFULLDOCOOKIES,		/* TCPReqQFullDoCookies */
 	LINUX_MIB_TCPREQQFULLDROP,		/* TCPReqQFullDrop */
 	LINUX_MIB_TCPRETRANSFAIL,		/* TCPRetransFail */
-	LINUX_MIB_TCPRCVCOALESCE,			/* TCPRcvCoalesce */
+	LINUX_MIB_TCPRCVCOALESCE,		/* TCPRcvCoalesce */
+	LINUX_MIB_TCPOFOQUEUE,			/* TCPOFOQueue */
+	LINUX_MIB_TCPOFODROP,			/* TCPOFODrop */
+	LINUX_MIB_TCPOFOMERGE,			/* TCPOFOMerge */
 	__LINUX_MIB_MAX
 };