Revert "net: Handle l3mdev in ip_tunnel_init_flow"

This reverts commit 760852df which is
commit db53cd3d 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: I3ceee98a4a56eb1c419109d369a6defd8b2f509b
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>