vxlan: Factor out device configuration

vxlan: Factor out device configuration

This factors out the device configuration out of the RTNL newlink
API which allows for in-kernel creation of VXLAN net_devices.

Orabug: 29755932

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 0dfbdf4102b9303d3ddf2177c0220098ff99f6de)

Reviewed-by: Rama Nichanamatlu <rama.nichanamatlu@oracle.com>
Signed-off-by: Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Conflicts:
	drivers/net/vxlan.c

Signed-off-by: Brian Maly <brian.maly@oracle.com>