Revert "net: vxlan: make vxlan_set_mac() return drop reasons"

This reverts commit e8919845 which is
commit d209706f upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: Ib2d834c688b8b2dc81c8803dee2b524f40d4ef1d
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>