6696 Per-client NFS server IOPS, bandwidth, and latency kstats

Review Request #171 — Created March 8, 2016 and updated — Latest diff uploaded

6472, 6476, 6696

webrev: http://cr.illumos.org/~webrev/marcel/il-nfs-kstat-per-client/

Support for detailed per-client and per-client/per-share IOPS, bandwidth, and latency kstats. This enhances (actually reimplements) the previous work done in #6090.

This implemenation fixes two bugs introduced by #6090:

6472 Panic in rfs4_compound_kstat_res()
6476 Taking exported_lock RW_READER lock in common_dispatch() can cause deadlock in nfssrv

I ran the NFS server with the implementation for several weeks with various NFS traffic to make sure everything works as expected.

In addition, I ran the mdb ::findleaks after the testing to make sure there are no memory leaks introduced.