Pxeboot - how to set network interface speed?

I can successfully do a PXE boot but the initial load of initrd and kernel is very slow because it drops back to 100Mbit instead of Gigabit. (This probably means it is actually causing all sorts of chaos with mismatched speed on the switch. It seems slower than I'd expect for even 100M) Once the kernel/initrd are loaded and it boots them, back up to gigabit speed. This is a boot config file I've used:

DEFAULT vesamenu.c32
PROMPT 0

# Option 1 - Local Boot 
LABEL bootlocal
    menu label ^Boot From Disk
    menu default
    LOCALBOOT -1

LABEL centos9
  menu label ^Network boot
  kernel images/centos9/vmlinuz
  append initrd=images/centos9/initrd.img ip=dhcp inst.ks=http://192.168.1.128/ks/client1.cfg 

Any ideas on how to set the interface to full duplex in the PXE environment?? Maybe some Lua script to set it?