fm10k: Add CONFIG_FM10K_VXLAN configuration option

Compiling with CONFIG_FM10K=y and VXLAN=m resulting in linking error:

   drivers/built-in.o: In function `fm10k_open':
   (.text+0x1f9d7a): undefined reference to `vxlan_get_rx_port'
   make: *** [vmlinux] Error 1

The fix follows the same strategy as I40E.

Signed-off-by: Andy Zhou <azhou@nicira.com>
Acked-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>