e1000: use disable_hardirq() for e1000_netpoll()

In commit 02cea395 ("genirq: Provide disable_hardirq()")
Peter introduced disable_hardirq() for netpoll, but it is forgotten
to use it for e1000.

This patch changes disable_irq() to disable_hardirq() for e1000.

Reported-by: Dave Jones <davej@codemonkey.org.uk>
Suggested-by: Sabrina Dubroca <sd@queasysnail.net>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>