Fix PCP issues found by Sebastien during code review

Fix PCP issues found by Sebastien during code review

- Resolve duplication of kernel.all.nprocs by switching
  one over to kernel.all.sysfork to match Linux PCP
- Add total physical memory metrics
- Fix units metadata for the kernel.all.nptys metric
- Drop not-yet-used network interface metric defitions
  (speed, baudrate, duplex)
- Correct the spelling of "celsius"
- Resolve confusion with rq_ticks/rd_ticks disk fields

Relates to https://github.com/sysstat/sysstat/pull/287