net: call skb_defer_free_flush() from __napi_busy_loop()

skb_defer_free_flush() is currently called from net_rx_action()
and napi_threaded_poll().

We should also call it from __napi_busy_loop() otherwise
there is the risk the percpu queue can grow until an IPI
is forced from skb_attempt_defer_free() adding a latency spike.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Samiullah Khawaja <skhawaja@google.com>
Acked-by: Stanislav Fomichev <sdf@google.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20240227210105.3815474-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>