MFC r240087:

MFC r240087:

Fix an error in setfacl(1) that manifested like this:

# setfacl -m u:trasz:rwx x
# setfacl -m u:root:rwx x
# getfacl x
# file: x
# owner: root
# group: wheel
user::rw-
user:root:rwx
user:trasz:rwx
group::r--
mask::rwx
other::r--
# setfacl -m u:root:rwx x
setfacl: x: acl_calc_mask() failed: Invalid argument
setfacl: x: failed to set ACL mask

For NFSv4 ACLs, this sort of situation would result in duplicated
entries.

git-svn-id: svn://svn.freebsd.org/base/stable/9@241187 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f