Revert "gtp: use exit_batch_rtnl() method"

This reverts commit 3d1c0c55 which is
commit 6eedda01 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: I580f707b263141595483cdc3f48e310264087d6e
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>