Add "gw" and "biosdevname" kernel params for pxe

"biosdevname=0" is needed in order to avoid random NIC naming on
some harware (DELL servers for example). "gw" paremeter is needed
for default route configuration. Also added "showmenu" param.

Change-Id: I57fb6f42fbd24adaa41cd2a99a59119c72c68a09
Merge "Add "gw" and "biosdevname" kernel params for pxe"