Revert "igb: reduce CPU0 latency when updating statistics"

This reverts commit 59361316.

Due to problems found in additional testing, this causes an illegal
context switch in the RCU read-side critical section.

CC: Dave Jones <davej@codemonkey.org.uk>
CC: Cong Wang <xiyou.wangcong@gmail.com>
CC: Jan Jablonsky <jan.jablonsky@thalesgroup.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>