9P: Use the flag in xattrcreate
FSAL_VFS: fix bad management of xattr. Assumption was made that xattr's contents were always plain strings
9P: new implementation of xattr. Allow acl to be written (setfacl is a disguised setfattr, it uses system.posix_acl_perms).
Merge remote-tracking branch 'ocre/dominique' into next

Conflicts:
	src/Protocols/9P/9p_xattrcreate.c