ovl: do operations on underlying file system in mounter's context

ovl: do operations on underlying file system in mounter's context

Given we are now doing checks both on overlay inode as well underlying
inode, we should be able to do checks and operations on underlying file
system using mounter's context.

So modify all operations to do checks/operations on underlying dentry/inode
in the context of mounter.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
[sw0312.kim: backport upstream commit 1175b6b8d96331676f1d436b089b965807f23b4a to resolve overlayfs smack deny issue]
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Change-Id: I550e2ed212f8a3a578cc48430556fa2c7e1eb3a2