917 Make TCP's iss_incr a tunable

*** 19,28 ****
--- 19,29 ----
   * 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.
*** 508,522 ****
          }
  
          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
                   * old connection.
                   *
                   * The next ISS generated is equal to tcp_iss_incr_extra
!                  * + 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
--- 509,523 ----
          }
  
          if ((flags & TH_SYN) && gap > 0 && rgap < 0) {
                  /*
                   * Make sure that when we accept the connection, pick
!                  * 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
!                  * + 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
*** 555,570 ****
                          /* 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;
                          break;
                  }
                  if ((adj = (int32_t)(tcp->tcp_snxt - new_iss)) > 0) {
                          /*
!                          * New ISS not guaranteed to be ISS_INCR/2
                           * ahead of the current tcp_snxt, so add the
                           * difference to tcp_iss_incr_extra.
                           */
                          tcps->tcps_iss_incr_extra += adj;
                  }
--- 556,572 ----
                          /* 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() *
!                             tcps->tcps_iss_incr;
                          break;
                  }
                  if ((adj = (int32_t)(tcp->tcp_snxt - new_iss)) > 0) {
                          /*
!                          * 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;
                  }