Properly invert the return of a strncmp call.

This was causing identification that should have been
made private to be public.

(closes issue AST-814)
reported by Patrick Anderson

Patches:
	chan_sip.c.diff uploaded by Patrick Anderson (license 5430)
........

Merged revisions 355268 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 355271 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@355274 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -15538,7 +15538,7 @@ static int get_pai(struct sip_pvt *p, struct sip_request *req)
 	}
 	ast_copy_string(privacy, sip_get_header(req, "Privacy"), sizeof(privacy));
-	if (!ast_strlen_zero(privacy) && strncmp(privacy, "id", 2)) {
+	if (!ast_strlen_zero(privacy) && !strncmp(privacy, "id", 2)) {
 		callingpres = AST_PRES_PROHIB_USER_NUMBER_NOT_SCREENED;
 	}
 	if (!cid_name) {