Real devices should implement qstats. Devices which support
pause or FEC configuration should also report the relevant stats.

nsim was missing FEC stats completely, some of the qstats
and pause stats required toggling a debugfs knob.

Note that the tests which used pause always initialize the setting
so they shouldn't be affected by the different starting value.
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>