lockd: Prepare share helpers for xdrgen conversion

lockd: Prepare share helpers for xdrgen conversion

In order to convert the NLMv4 server-side XDR functions to use
xdrgen, the internal share helpers need to be decoupled from the
NLMv3-specific struct nlm_args. NLMv4 procedures will use
different argument structures once they are converted.

Refactor nlmsvc_share_file() and nlmsvc_unshare_file() to accept
individual arguments (oh, access, mode) instead of the common
struct nlm_args. This allows both protocol versions to call these
helpers without forcing a common argument structure.

While here, add kdoc comments to both functions and fix a comment
typo in the unshare path.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>