Add a simple mechanism for collecting stats in the RPC client. Stats are
tabulated during xprt_release. Note that per_cpu shenanigans are not
required here because the RPC client already serializes on the transport
write lock.
Test plan:
Compile kernel with CONFIG_NFS enabled. Basic performance regression
testing with high-speed networking and high performance server.
Signed-off-by: Chuck Lever <cel@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
