ss: print value of IPV6_V6ONLY socket option if set

If available and set, print 'v6only:1' for AF_INET6 sockets upon request
of extended information. For IPv6 sockets bound to in6addr_any, this is
the only way to determine if they will also accept IPv4 requests or not.
Signed-off-by: Phil Sutter <phil@nwl.cc>

misc/ss.c

@@ -2045,6 +2045,11 @@ static int inet_show_sock(struct nlmsghdr *nlh, struct filter *f, int protocol)
 
 	if (show_details) {
 		sock_details_print(&s);
+		if (s.local.family == AF_INET6 && tb[INET_DIAG_SKV6ONLY]) {
+			unsigned char v6only;
+			v6only = *(__u8 *)RTA_DATA(tb[INET_DIAG_SKV6ONLY]);
+			printf(" v6only:%u", v6only);
+		}
 		if (tb[INET_DIAG_SHUTDOWN]) {
 			unsigned char mask;
 			mask = *(__u8 *)RTA_DATA(tb[INET_DIAG_SHUTDOWN]);