net: add dev_dstats_rx_dropped_add() helper

Introduce the dev_dstats_rx_dropped_add() helper to allow incrementing
the rx_drops per-CPU statistic by an arbitrary value, rather than just
one. This is useful for drivers or code paths that need to account for
multiple dropped packets at once, such as when dropping entire queues.

Reviewed-by: Joe Damato <joe@dama.to>
Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20250618-netdevsim_stat-v4-3-19fe0d35e28e@debian.org


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