net: 3com: 3c59x: irq save variant of ISR

When vortex_boomerang_interrupt() is invoked from vortex_tx_timeout() or
poll_vortex() interrupts must be disabled. This detaches the interrupt
disable logic from locking which requires patching for PREEMPT_RT.

The advantage of avoiding spin_lock_irqsave() in the interrupt handler is
minimal, but converting it removes all the extra code for callers which
come not from interrupt context.

Cc: Steffen Klassert <klassert@mathematik.tu-chemnitz.de>
Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>