sunrpc: Add a sysfs files for rpc_clnt information

These files display useful information about the RPC client, such as the
rpc version number, program name, and maximum number of connections
allowed.

Reviewed-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
Link: https://lore.kernel.org/r/20250207204225.594002-4-anna@kernel.org


Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>