Merge r293013 from clang380-import branch:

Fix a clang 3.8.0 warning in pflogd.c:

contrib/pf/pflogd/pflogd.c:769:8: error: logical not is only applied to the left hand side of this comparison [-Werror,-Wlogical-not-parentheses]
			if (!if_exists(interface) == -1) {
			    ^                     ~~

The if_exists() function does not return -1, and even if it did, it
would not be the correct way to check.  Just ditch the == -1 instead.

Obtained from:	OpenBSD's pflogd.c 1.49
MFC after:	3 days

contrib/pf/pflogd/pflogd.c

@@ -766,7 +766,7 @@ main(int argc, char **argv)
 		np = pcap_dispatch(hpcap, PCAP_NUM_PKTS,
 		    phandler, (u_char *)dpcap);
 		if (np < 0) {
-			if (!if_exists(interface) == -1) {
+			if (!if_exists(interface)) {
 				logmsg(LOG_NOTICE, "interface %s went away",
 				    interface);
 				ret = -1;