vfs: export __inode_permission() to modules

We need to be able to check inode permissions (but not filesystem implied
permissions) for stackable filesystems.  Expose this interface for overlayfs.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

diff --cc fs/internal.h
Simple merge

diff --cc fs/namei.c
Simple merge

diff --cc include/linux/fs.h
Simple merge