add kstat support for reading the "hardware" counters for each ring.

the counters happen to be a series of uint64_t values in memory,
so we treat them as arrays that get mapped to a series of kstat_kv
structs that are set up as 64 bit counters with either packet or
byte counters as appropriate. this helps keep the code size down.

while we export the counters as separate kstats per rx and tx ring,
you request an update from the hypervisor at the controller level.
this code ratelimits these requests to 1 per second per interface
to try and debounce this a bit so each kstat read doesnt cause a
vmexit.

here's an example of the stats. note that we get to see how many
packets that rx ring moderation drops for the first time. see the
"no buffers" stat.

vmx0:0:rxq:5
         packets: 2372483 packets
           bytes: 3591909057 bytes
          qdrops: 0 packets
          errors: 0 packets
            qlen: 0 packets
...
vmx0:0:txq:5
         packets: 1316856 packets
           bytes: 86961577 bytes
          qdrops: 0 packets
          errors: 0 packets
            qlen: 1 packets
         maxqlen: 512 packets
         oactive: false
...
vmx0:0:vmx-rxstats:5
     LRO packets: 0 packets
       LRO bytes: 0 bytes
   ucast packets: 2372483 packets
     ucast bytes: 3591909053 bytes
   mcast packets: 0 packets
     mcast bytes: 0 bytes
   bcast packets: 0 packets
     bcast bytes: 0 bytes
      no buffers: 696 packets
          errors: 0 packets
...
vmx0:0:vmx-txstats:5
     TSO packets: 0 packets
       TSO bytes: 0 bytes
   ucast packets: 1316839 packets
     ucast bytes: 86960455 bytes
   mcast packets: 0 packets
     mcast bytes: 0 bytes
   bcast packets: 0 packets
     bcast bytes: 0 bytes
          errors: 0 packets
        discards: 0 packets

0 files changed, 0 insertions, 0 deletions