sys/linux: make some fscrypt ioctls take fd_dir
sys/linux: make some fscrypt ioctls take fd_dir

Make ioctls take fd_dir rather than fd when they are primarily intended
to be used on directories.  Especially for FS_IOC_SET_ENCRYPTION_POLICY,
this should increase the chance that syzkaller does something useful
with these ioctls.

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