NFSv4.1 enforce rootpath check in fs_location query

[ Upstream commit 28568c90 ]

In commit 4ca9f31a ("NFSv4.1 test and add 4.1 trunking transport"),
we introduce the ability to query the NFS server for possible trunking
locations of the existing filesystem. However, we never checked the
returned file system path for these alternative locations. According
to the RFC, the server can say that the filesystem currently known
under "fs_root" of fs_location also resides under these server
locations under the following "rootpath" pathname. The client cannot
handle trunking a filesystem that reside under different location
under different paths other than what the main path is. This patch
enforces the check that fs_root path and rootpath path in fs_location
reply is the same.

Fixes: 4ca9f31a ("NFSv4.1 test and add 4.1 trunking transport")
Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>