pf: fix memory leak

The nvlist is allocated in pf_keth_rule_to_nveth_rule(). There's no need
to allocate one in the calling function. Especially not as we overwrite
the pointer to the new nvlist with the one allocated by
pf_keth_rule_to_nveth_rule(), leaking memory.

Reported by:	Coverity
CID:		1476128
Sponsored by:	Rubicon Communications, LLC ("Netgate")

sys/netpfil/pf/pf_ioctl.c

@@ -2720,8 +2720,6 @@ DIOCGETETHRULES_error:
 		free(nvlpacked, M_TEMP);
 		nvlpacked = NULL;
 
-		nvl = nvlist_create(0);
-
 		rule = TAILQ_FIRST(rs->active.rules);
 		while ((rule != NULL) && (rule->nr != nr))
 			rule = TAILQ_NEXT(rule, entries);