nfs: fix the fetch of FATTR4_OPEN_ARGUMENTS

The client doesn't properly request FATTR4_OPEN_ARGUMENTS in the initial
SERVER_CAPS getattr. Add FATTR4_WORD2_OPEN_ARGUMENTS to the initial
request.

Fixes: 707f13b3 (NFSv4: Add support for the FATTR4_OPEN_ARGUMENTS attribute)
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>