mpls: fix af_mpls dependencies

MPLS routing code relies on sysctl to work, so let it select PROC_SYSCTL.
Reported-by: NRandy Dunlap <rdunlap@infradead.org>
Suggested-by: NDavid Ahern <dsahern@gmail.com>
Signed-off-by: NMatteo Croce <mcroce@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/mpls/Kconfig

@@ -26,6 +26,7 @@ config NET_MPLS_GSO
 config MPLS_ROUTING
 	tristate "MPLS: routing support"
 	depends on NET_IP_TUNNEL || NET_IP_TUNNEL=n
+	select PROC_SYSCTL
 	---help---
 	 Add support for forwarding of mpls packets.