syscalls/swapoff: Further cleanup.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
syscalls/swapoff01: Do not fail on Btrfs

Currently swapfiles on Btrfs are not supported and I've been told that
it's not likely to be implemented in the near future.

So if we are on Btrfs and we get EINVAL from swapon() we return TCONF.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
syscalls/swapon: Further cleanup.

* Sort out included files

* Use safe macros

* etc

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
syscalls/swapon: Do not fail on Btrfs

Currently swapfiles on Btrfs are not supported and I've been told that
it's not likely to be implemented in the near future.

So if we are on Btrfs and we get EINVAL from swapon() we return TCONF.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>