917 Make TCP's iss_incr a tunable

*** 3925,3935 ****
          struct { uint32_t ports; in6_addr_t src; in6_addr_t dst; } arg;
          uint32_t answer[4];
          tcp_stack_t     *tcps = tcp->tcp_tcps;
          conn_t          *connp = tcp->tcp_connp;
  
!         tcps->tcps_iss_incr_extra += (ISS_INCR >> 1);
          tcp->tcp_iss = tcps->tcps_iss_incr_extra;
          switch (tcps->tcps_strong_iss) {
          case 2:
                  mutex_enter(&tcps->tcps_iss_key_lock);
                  context = tcps->tcps_iss_key;
--- 3925,3935 ----
          struct { uint32_t ports; in6_addr_t src; in6_addr_t dst; } arg;
          uint32_t answer[4];
          tcp_stack_t     *tcps = tcp->tcp_tcps;
          conn_t          *connp = tcp->tcp_connp;
  
!         tcps->tcps_iss_incr_extra += (tcps->tcps_iss_incr >> 1);
          tcp->tcp_iss = tcps->tcps_iss_incr_extra;
          switch (tcps->tcps_strong_iss) {
          case 2:
                  mutex_enter(&tcps->tcps_iss_key_lock);
                  context = tcps->tcps_iss_key;
*** 3948,3958 ****
                  /* FALLTHRU */
          case 1:
                  tcp->tcp_iss += (gethrtime() >> ISS_NSEC_SHT) + tcp_random();
                  break;
          default:
!                 tcp->tcp_iss += (uint32_t)gethrestime_sec() * ISS_INCR;
                  break;
          }
          tcp->tcp_valid_bits = TCP_ISS_VALID;
          tcp->tcp_fss = tcp->tcp_iss - 1;
          tcp->tcp_suna = tcp->tcp_iss;
--- 3948,3959 ----
                  /* FALLTHRU */
          case 1:
                  tcp->tcp_iss += (gethrtime() >> ISS_NSEC_SHT) + tcp_random();
                  break;
          default:
!                 tcp->tcp_iss += (uint32_t)gethrestime_sec() *
!                     tcps->tcps_iss_incr;
                  break;
          }
          tcp->tcp_valid_bits = TCP_ISS_VALID;
          tcp->tcp_fss = tcp->tcp_iss - 1;
          tcp->tcp_suna = tcp->tcp_iss;