917 Make TCP's iss_incr a tunable

@@ -3925,11 +3925,11 @@
         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);
+        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;

@@ -3948,11 +3948,12 @@
                 /* FALLTHRU */
         case 1:
                 tcp->tcp_iss += (gethrtime() >> ISS_NSEC_SHT) + tcp_random();
                 break;
         default:
-                tcp->tcp_iss += (uint32_t)gethrestime_sec() * ISS_INCR;
+                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;