net/e1000: fix forced configuration of speed and duplex

net/e1000: fix forced configuration of speed and duplex

From the code, it looks like, hw->mac.autoneg, variable is used to
switch between calling either autoneg function or forcing
speed/duplex function. But this variable is not modified in
eth_em_start/eth_igb_start routines (it is always set to 1)
even while forcing the link speed.

Following discussion thread has some more information on this:
http://dpdk.org/ml/archives/dev/2016-October/049272.html

Signed-off-by: Ananda Sathyanarayana <ananda@versa-networks.com>
Acked-by: Wenzhuo Lu <wenzhuo.lu@intel.com>