Revert "netfilter: rpfilter/fib: Populate flowic_l3mdev field"

This reverts commit 5c6cb7ab which is
commit acc641ab 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: I44a61f2a2600d2cd4b624ef826844eb6360797c7
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>