917 Make TCP's iss_incr a tunable

@@ -19,10 +19,11 @@
  * CDDL HEADER END
  */
 
 /*
  * Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2011, Joyent Inc. All rights reserved.
  */
 
 /*
  * This file contains functions related to TCP time wait processing.  Also
  * refer to the time wait handling comments in tcp_impl.h.

@@ -508,15 +509,15 @@
         }
 
         if ((flags & TH_SYN) && gap > 0 && rgap < 0) {
                 /*
                  * Make sure that when we accept the connection, pick
-                 * an ISS greater than (tcp_snxt + ISS_INCR/2) for the
+                 * an ISS greater than (tcp_snxt + tcp_iss_incr/2) for the
                  * old connection.
                  *
                  * The next ISS generated is equal to tcp_iss_incr_extra
-                 * + ISS_INCR/2 + other components depending on the
+                 * + tcp_iss_incr/2 + other components depending on the
                  * value of tcp_strong_iss.  We pre-calculate the new
                  * ISS here and compare with tcp_snxt to determine if
                  * we need to make adjustment to tcp_iss_incr_extra.
                  *
                  * The above calculation is ugly and is a

@@ -555,16 +556,17 @@
                         /* Add time component and min random (i.e. 1). */
                         new_iss += (gethrtime() >> ISS_NSEC_SHT) + 1;
                         break;
                 default:
                         /* Add only time component. */
-                        new_iss += (uint32_t)gethrestime_sec() * ISS_INCR;
+                        new_iss += (uint32_t)gethrestime_sec() *
+                            tcps->tcps_iss_incr;
                         break;
                 }
                 if ((adj = (int32_t)(tcp->tcp_snxt - new_iss)) > 0) {
                         /*
-                         * New ISS not guaranteed to be ISS_INCR/2
+                         * New ISS not guaranteed to be tcp_iss_incr/2
                          * ahead of the current tcp_snxt, so add the
                          * difference to tcp_iss_incr_extra.
                          */
                         tcps->tcps_iss_incr_extra += adj;
                 }