Fix interaction between userns uid/gid and SA

Fix interaction between userns uid/gid and SA

* When the uid/gid change is handled in zfs_setattr we want to
actually adjust the user passed uid to a KUID and write that to disk.

* In trace points use the i_uid member without doing translation,
since it has already been performed.

* Use kuid in zfs_aclset_common

Signed-off-by: Nikolay Borisov <n.borisov.lkml@gmail.com>
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #4928