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

This reverts commit 5cf22915 which is
commit 289fd4e7 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: Icf1c0dc0edaeba2841bc043baa327b060dabfd2c
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>