staging: lustre: llite: break ll_getxattr_common into 2 functions

Split the function ll_getxattr_common into two functions.
The code used for listing xattrs and ll_getxattr_common is
placed into a new function ll_getxattr_list. This allows
ll_listxattr to call directly ll_getxattr_list instead of
going through ll_getxattr_common. This change is needed
for the upcoming VFS move xattr_handler from [s|g]etxattr.

Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>