sockets: don't block IPv4 clients when listening on "::"

When inet_parse() parses the hostname, it is forcing the
has_ipv6 && ipv6 flags if the address contains a ":". This
means that if the user had set the ipv4=on flag, to try to
restrict the listener to just ipv4, an error would not have
been raised.  eg

   -incoming tcp:[::]:9000,ipv4

should have raised an error because listening for IPv4
on "::" is a non-sensical combination. With this removed,
we now call getaddrinfo() on "::" passing PF_INET and
so getaddrinfo reports an error about the hostname being
incompatible with the requested protocol:

 qemu-system-x86_64: -incoming tcp:[::]:9000,ipv4: address resolution
    failed for :::9000: Address family for hostname not supported

Likewise it is explicitly setting the has_ipv4 & ipv4
flags when the address contains only digits + '.'. This
has no ill-effect, but also has no benefit, so is removed.
Acked-by: NGerd Hoffmann <kraxel@gmail.com>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

util/qemu-sockets.c

@@ -618,16 +618,12 @@ int inet_parse(InetSocketAddress *addr, const char *str, Error **errp)
             error_setg(errp, "error parsing IPv6 address '%s'", str);
             return -1;
         }
-        addr->ipv6 = addr->has_ipv6 = true;
     } else {
         /* hostname or IPv4 addr */
         if (sscanf(str, "%64[^:]:%32[^,]%n", host, port, &pos) != 2) {
             error_setg(errp, "error parsing address '%s'", str);
             return -1;
         }
-        if (host[strspn(host, "0123456789.")] == '\0') {
-            addr->ipv4 = addr->has_ipv4 = true;
-        }
     }
 
     addr->host = g_strdup(host);