Revert "net: Fix netns for ip_tunnel_init_flow()"

This reverts commit d4b3978f which is
commit b5a7b661 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: Ic00e232a1b76645e8c5ba32610cc4d896e00ef6e
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>