netpoll: fix netconsole IPv6 setup

Currently, to make netconsole start over IPv6, the source address
needs to be specified. Without a source address, netpoll_parse_options
assumes we're setting up over IPv4 and the destination IPv6 address is
rejected.

Check if the IP version has been forced by a source address before
checking for a version mismatch when parsing the destination address.
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Acked-by: Cong Wang <cwang@twopensource.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/netpoll.c

@@ -948,6 +948,7 @@ int netpoll_parse_options(struct netpoll *np, char *opt)
 {
 	char *cur=opt, *delim;
 	int ipv6;
+	bool ipversion_set = false;
 
 	if (*cur != '@') {
 		if ((delim = strchr(cur, '@')) == NULL)
@@ -960,6 +961,7 @@ int netpoll_parse_options(struct netpoll *np, char *opt)
 	cur++;
 
 	if (*cur != '/') {
+		ipversion_set = true;
 		if ((delim = strchr(cur, '/')) == NULL)
 			goto parse_failed;
 		*delim = 0;
@@ -1002,7 +1004,7 @@ int netpoll_parse_options(struct netpoll *np, char *opt)
 	ipv6 = netpoll_parse_ip_addr(cur, &np->remote_ip);
 	if (ipv6 < 0)
 		goto parse_failed;
-	else if (np->ipv6 != (bool)ipv6)
+	else if (ipversion_set && np->ipv6 != (bool)ipv6)
 		goto parse_failed;
 	else
 		np->ipv6 = (bool)ipv6;