sys/linux: update smack descriptions
sys/linux: update smack descriptions

Add descriptions for /sys/fs/smackfs/* interfaces.

Signed-off-by: Denis Efremov <accabd4edc44e4dbbf4e6307bae515853f535251@linux.com>

xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller