Witold Kręcicki authored Jan 04, 2019 and Ondřej Surý committed Apr 25, 2019

the TCP client quota could still be ineffective under some
circumstances.  this change:

- improves quota accounting to ensure that TCP clients are
  properly limited, while still guaranteeing that at least one client
  is always available to serve TCP connections on each interface.
- uses more descriptive names and removes one (ntcptarget) that
  was no longer needed
- adds comments

(cherry picked from commit 924651f1)
(cherry picked from commit 55a7a458)