SUNRPC: Add trace_rpc_timeout_status()

For a long while we've wanted a tracepoint that fires when a major
timeout is reported in the system log. Such a tracepoint can be
attached to other actions that can take place when a timeout is
detected (eg, server or connection health assessment).

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>