[NETFILTER]: sip conntrack: make header shortcuts optional

Not every header has a shortcut, so make them optional instead
of searching for the same string twice.

Signed-off-by: Patrick McHardy <kaber@trash.net>
diff --git a/net/ipv4/netfilter/ip_conntrack_sip.c b/net/ipv4/netfilter/ip_conntrack_sip.c
index a9c0d1d3..0a6a13c4 100644
--- a/net/ipv4/netfilter/ip_conntrack_sip.c
+++ b/net/ipv4/netfilter/ip_conntrack_sip.c
@@ -72,8 +72,6 @@
 	[POS_REQ_HEADER] = { 	/* SIP Requests headers */
 		.lname		= "sip:",
 		.lnlen		= sizeof("sip:") - 1,
-		.sname		= "sip:",
-		.snlen		= sizeof("sip:") - 1, /* yes, i know.. ;) */
 		.ln_str		= "@",
 		.ln_strlen	= sizeof("@") - 1,
 		.match_len	= epaddr_len
@@ -286,7 +284,8 @@
 
 	while (dptr <= limit) {
 		if ((strncmp(dptr, hnfo->lname, hnfo->lnlen) != 0) &&
-		    (strncmp(dptr, hnfo->sname, hnfo->snlen) != 0)) {
+		    (hinfo->sname == NULL ||
+		     strncmp(dptr, hnfo->sname, hnfo->snlen) != 0)) {
 			dptr++;
 			continue;
 		}