libpfctl: fix label setting

A mismerge caused the labels list to be added to the wrong nvlist,
breaking label configuration.

If you compare the change from from main and stable/13 you
can see that main uses "nvl" and stable/13 has "nlvr" for
nvlist_append_string_array() but the backport changes it to "nlv".

This code was supposed to apply to pfctl_add_eth_rule() but instead
applied to pfctl_add_rule() for otherwise interesting reasons.  Since
pfctl_add_eth_rule() uses "nvl" and pfctl_add_rule() uses "nvlr" but
also has "nvl" this compiled fine but still broke the label set.

Direct commit to stable/13.

PR:		275006

lib/libpfctl/libpfctl.c

@@ -643,7 +643,7 @@ pfctl_add_rule(int dev, const struct pfctl_rule *r, const char *anchor,
 	labelcount = 0;
 	while (labelcount < PF_RULE_MAX_LABEL_COUNT &&
 	    r->label[labelcount][0] != 0) {
-		nvlist_append_string_array(nvl, "labels",
+		nvlist_append_string_array(nvlr, "labels",
 		    r->label[labelcount]);
 		labelcount++;
 	}