security: rework selinux, smack, ima, apparmor detection logic

Always cache the results, and bypass low-level security calls when
the respective subsystem is not enabled.

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>
smack: minimize ifdef use, and move all labeling to smack-util.c

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>
udev: usb_id - remove obsoleted bInterfaceSubClass == 5 match

bInterfaceSubClass == 5 is not a "floppy"; just identify the obsolete
QIC-157 interface as "generic".

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>
Fix write-only use of a few variables

Since the invention of read-only memory, write-only memory has been
considered deprecated. Where appropriate, either make use of the
value, or avoid writing it, to make it clear that it is not used.

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>
udev: use initialization instead of zeroing in one place

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>