doc: net: napi: Update documentation for napi_schedule_irqoff

doc: net: napi: Update documentation for napi_schedule_irqoff

Since commit 8380c81d5c4f ("net: Treat __napi_schedule_irqoff() as
__napi_schedule() on PREEMPT_RT"), napi_schedule_irqoff will do the
right thing if IRQs are threaded. Therefore, there is no need to use
IRQF_NO_THREAD.

Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20240930153955.971657-1-sean.anderson@linux.dev
Signed-off-by: Paolo Abeni <pabeni@redhat.com>