Shorten text string for ip_fw2 dynamic rules zone by removing the word

"zone", which is generally not present in zone names.  This reduces the
incidence of line-wrapping in "vmstat -z " using 80-column displays.

MFC after:	3 days

sys/netinet/ip_fw2.c

@@ -4891,7 +4891,7 @@ ipfw_init(void)
 
 	layer3_chain.rules = NULL;
 	IPFW_LOCK_INIT(&layer3_chain);
-	ipfw_dyn_rule_zone = uma_zcreate("IPFW dynamic rule zone",
+	ipfw_dyn_rule_zone = uma_zcreate("IPFW dynamic rule",
 	    sizeof(ipfw_dyn_rule), NULL, NULL, NULL, NULL,
 	    UMA_ALIGN_PTR, 0);
 	IPFW_DYN_LOCK_INIT();