mpls: Fix the openvswitch select of NET_MPLS_GSO

Fix the OPENVSWITCH Kconfig option and old Kconfigs by having
OPENVSWITCH select both NET_MPLS_GSO and MPLSO.

A Kbuild test robot reported that when NET_MPLS_GSO is selected by
OPENVSWITCH the generated .config is broken because MPLS is not
selected.

Cc: Simon Horman <[e-mail]>
Fixes: cec9166ca4e mpls: Refactor how the mpls module is built
Reported-by: kbuild test robot <[e-mail]>
Signed-off-by: "Eric W. Biederman" <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/openvswitch/Kconfig

···
 	tristate "Open vSwitch"
 	depends on INET
 	select LIBCRC32C
+	select MPLS
 	select NET_MPLS_GSO
 	---help---
 	  Open vSwitch is a multilayer Ethernet switch targeted at virtualized