e1000e: extend timeout for ethtool link test diagnostic

With some PHYs supported by this driver, link establishment can take a
little longer when connected to certain switches.  Extend the timeout to
reduce the number of false diagnostic failures, and cleanup a code style
issue in the same function.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>