Revert "gtp: use exit_batch_rtnl() method"

This reverts commit 85d96633 which is
commit 6eedda01b2bfdcf427b37759e053dc27232f3af1 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: Idcdef934cbbe6566d020c84086f33964fb30e1e9
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>