[TCP]: MTU probing

Implementation of packetization layer path mtu discovery for TCP, based on
the internet-draft currently found at
<http://www.ietf.org/internet-drafts/draft-ietf-pmtud-method-05.txt>.

Signed-off-by: John Heffner <jheffner@psc.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inet_connection_sock.h

@@ -72,6 +72,7 @@ struct inet_connection_sock_af_ops {
  * @icsk_probes_out:	   unanswered 0 window probes
  * @icsk_ext_hdr_len:	   Network protocol overhead (IP/IPv6 options)
  * @icsk_ack:		   Delayed ACK control data
+ * @icsk_mtup;		   MTU probing control data
  */
 struct inet_connection_sock {
 	/* inet_sock has to be the first member! */
@@ -104,6 +105,18 @@ struct inet_connection_sock {
 		__u16		  last_seg_size; /* Size of last incoming segment	   */
 		__u16		  rcv_mss;	 /* MSS used for delayed ACK decisions	   */ 
 	} icsk_ack;
+	struct {
+		int		  enabled;
+
+		/* Range of MTUs to search */
+		int		  search_high;
+		int		  search_low;
+
+		/* Information on the current probe. */
+		int		  probe_size;
+		__u32		  probe_seq_start;
+		__u32		  probe_seq_end;
+	} icsk_mtup;
 	u32			  icsk_ca_priv[16];
 #define ICSK_CA_PRIV_SIZE	(16 * sizeof(u32))
 };