e1000e: reset swflag after resetting hardware

in the process of debugging things, noticed that the swflag is not reset
by the driver after reset, and the swflag is probably not reset unless
management firmware clears it after 100ms.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>