917 Make TCP's iss_incr a tunable

@@ -495,10 +495,11 @@
 #define tcps_keepalive_abort_interval_low \
                                         tcps_propinfo_tbl[56].prop_min_uval
 #define tcps_wroff_xtra                 tcps_propinfo_tbl[57].prop_cur_uval
 #define tcps_dev_flow_ctl               tcps_propinfo_tbl[58].prop_cur_bval
 #define tcps_reass_timeout              tcps_propinfo_tbl[59].prop_cur_uval
+#define tcps_iss_incr                   tcps_propinfo_tbl[65].prop_cur_uval
 
 extern struct qinit tcp_rinitv4, tcp_rinitv6;
 extern boolean_t do_tcp_fusion;
 
 /*