kernel/modules: add native vxlan package

kernel/modules: add native vxlan package

More recent kernel versions (>= 3.12) support native VXLAN
support.

The Open VSwitch kernel module tries to build using native VXLAN
support if it detects a kernel version >=3.12.

The build works fine, but during startup the OVS kernel module
does not load.
dmesg output is something like this:
    [ 1201.262842] openvswitch: Unknown symbol vxlan_sock_release
    [ 1201.262949] openvswitch: Unknown symbol vxlan_xmit_skb
    [ 1201.263161] openvswitch: Unknown symbol vxlan_sock_add

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43126 3c298f89-4303-0410-b956-a3cf2f4a3e73