btrfs: use generic posix ACL infrastructure

Also don't bother to set up a .get_acl method for symlinks as we do not
support access control (ACLs or even mode bits) for symlinks in Linux.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --cc fs/btrfs/acl.c
Simple merge

diff --cc fs/btrfs/ctree.h
Simple merge

diff --cc fs/btrfs/inode.c
Simple merge

diff --cc fs/btrfs/xattr.c
Simple merge

diff --cc fs/btrfs/xattr.h
Simple merge