netdevsim: collect statistics at RX side

When the RX side of netdevsim was added, the RX statistics were missing,
making the driver unusable for GenerateTraffic() test framework.

This patch adds proper statistics tracking on RX side, complementing the
TX path.

Reviewed-by: Joe Damato <joe@dama.to>
Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20250618-netdevsim_stat-v4-2-19fe0d35e28e@debian.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>