efi_loader: completely initialize network

Add missing network initialization code.

Before the patch the network was only usable if a network command like
dhcp or tftp had beed executed.

This was visible when interrupting the console countdown and executing
bootefi selftest for vexpress_ca15_tc2_defconfig.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>