NFS: Refactor trace_nfs4_offload_cancel

NFS: Refactor trace_nfs4_offload_cancel

Add a trace_nfs4_offload_status trace point that looks just like
trace_nfs4_offload_cancel. Promote that event to an event class to
avoid duplicating code.

An alternative approach would be to expand trace_nfs4_offload_status
to report more of the actual OFFLOAD_STATUS result.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Benjamin Coddington <bcodding@redhat.com>
Link: https://lore.kernel.org/r/20250113153235.48706-16-cel@kernel.org
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>