staging: qlge: Remove irq_cnt

staging: qlge: Remove irq_cnt

qlge uses an irq enable/disable refcounting scheme that is:
* poorly implemented
	Uses a spin_lock to protect accesses to the irq_cnt atomic
	variable.
* buggy
	Breaks when there is not a 1:1 sequence of irq - napi_poll, such as
	when using SO_BUSY_POLL.
* unnecessary
	The purpose or irq_cnt is to reduce irq control writes when
	multiple work items result from one irq: the irq is re-enabled
	after all work is done.
	Analysis of the irq handler shows that there is only one case where
	there might be two workers scheduled at once, and those have
	separate irq masking bits.

Therefore, remove irq_cnt.

Additionally, we get a performance improvement:
perf stat -e cycles -a -r5 super_netperf 100 -H 192.168.33.1 -t TCP_RR

Before:
628560
628056
622103
622744
627202
[...]
   268,803,947,669      cycles                 ( +-  0.09% )

After:
636300
634106
634984
638555
634188
[...]
   259,237,291,449      cycles                 ( +-  0.19% )

Signed-off-by: Benjamin Poirier <bpoirier@suse.com>
Link: https://lore.kernel.org/r/20190927101210.23856-3-bpoirier@suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>