util: Add AF_UNSPEC support to sockaddr_ntop()

Allow sockaddr_ntop() to format AF_UNSPEC socket addresses.  There do exist
a few cases where we might legitimately have either an AF_UNSPEC or a real
address, such as the origin address from MSG_ERRQUEUE.  Even in cases where
we shouldn't get an AF_UNSPEC address, formatting it is likely to make
things easier to debug if we ever somehow do.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

util.c

@@ -622,6 +622,10 @@ const char *sockaddr_ntop(const void *sa, char *dst, socklen_t size)
 	} while (0)
 
 	switch (family) {
+	case AF_UNSPEC:
+		IPRINTF("<unspecified>");
+		break;
+
 	case AF_INET: {
 		const struct sockaddr_in *sa4 = sa;