boot: call dhcp_run in pxe bootmethod

boot: call dhcp_run in pxe bootmethod

A recent change tried to speed up EFI booting by not calling dhcp_run
from eth_bootdev_hunt() every time. PXE so far relied on that dhcp_run
call to get an IP address.

Fix that by adding a dhcp_run call to the pxe bootflow, with autoload
disabled to only get the ip address and nothing else.

Suggested-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Fixes: 1f68057e0320 ("net: eth_bootdev_hunt() should not run DHCP")
Signed-off-by: Heiko Stuebner <heiko@sntech.de>