posix_acl: Add set_posix_acl

posix_acl: Add set_posix_acl

[ Upstream commit 485e71e8fb6356c08c7fc6bcce4bf02c9a9a663f ]

Factor out part of posix_acl_xattr_set into a common function that takes
a posix_acl, which nfsd can also call.

The prototype already exists in include/linux/posix_acl.h.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Cc: stable@vger.kernel.org
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>