net/cpsw: fix irq_disable() with threaded interrupts

During high throughput it is likely that we receive both: an RX and TX
interrupt. The normal behaviour is that once we enter the ISR the
interrupts are disabled in the IRQ chip and so the ISR is invoked only
once and the interrupt line is disabled once. It will be re-enabled
after napi completes.
With threaded interrupts on the other hand the interrupt the interrupt
is disabled immediately and the ISR is marked for "later". By having TX
and RX interrupt marked pending we invoke them both and disable the
interrupt line twice. The napi callback is still executed once and so
after it completes we remain with interrupts disabled.

The initial patch simply removed the cpsw_{enable|disable}_irq() calls
and it worked well on my AM335X ES1.0 (beagle bone). On ES2.0 (beagle
bone black) it caused an never ending interrupt (even after the mask via
cpsw_intr_disable()) according to Mugunthan V N. Since I don't have the
ES2.0 and no idea what is going on this patch tracks the state of the
irq_disable() call and execute it only when not yet done.
The book keeping is done on the first struct since with dual_emac we can
have two of those and only one interrupt line.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>