NFSv4.1: use EXCHGID4_FLAG_USE_PNFS_DS for DS server

[ Upstream commit 51d674a5 ]

After receiving the location(s) of the DS server(s) in the
GETDEVINCEINFO, create the request for the clientid to such
server and indicate that the client is connecting to a DS.

Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Stable-dep-of: 806a3bc4 ("NFSv4.1: fix pnfs MDS=DS session trunking")
Signed-off-by: Sasha Levin <sashal@kernel.org>