mlxsw: spectrum: Add VXLAN dependency for spectrum

When VXLAN is a loadable module, MLXSW_SPECTRUM must not be built-in:

drivers/net/ethernet/mellanox/mlxsw/spectrum_switchdev.c:2547: undefined
reference to `vxlan_fdb_find_uc'

Add Kconfig dependency to enforce usable configurations.

Fixes: 1231e04f ("mlxsw: spectrum_switchdev: Add support for VxLAN encapsulation")
Signed-off-by: NIdo Schimmel <idosch@mellanox.com>
Reported-by: Nkbuild test robot <lkp@intel.com>
Reviewed-by: NPetr Machata <petrm@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/Kconfig

@@ -78,6 +78,7 @@ config MLXSW_SPECTRUM
 	depends on IPV6 || IPV6=n
 	depends on NET_IPGRE || NET_IPGRE=n
 	depends on IPV6_GRE || IPV6_GRE=n
+	depends on VXLAN || VXLAN=n
 	select GENERIC_ALLOCATOR
 	select PARMAN
 	select OBJAGG