Can't set CONFIG_IP_PNP on the ramips kernel

Hi,

I'm trying to setup network booting on the ramips kernel but when I try and enable CONFIG_IP_PNP is gets unselected when the Kernel is configured. I'm running from the openwrt-19.07 branch.

I ran
make kernel_menuconfig
enable the relevant configuration items and save and then in
target/linux/ramips/mt76x8/config-4.14
I have the new configuration parameters

CONFIG_IP_PNP=y
# CONFIG_IP_PNP_BOOTP is not set
CONFIG_IP_PNP_DHCP=y
# CONFIG_IP_PNP_RARP is not set
CONFIG_NFS_ACL_SUPPORT=y
CONFIG_NFS_FS=y
CONFIG_NFS_V2=y
CONFIG_NFS_V3_ACL=y
CONFIG_ROOT_NFS=y

But when I build the kernel it fails to boot over the network and after checking the .config file that is created I see

# CONFIG_IP_PNP is not set

The other parameters have been set except for ROOT_NFS as this depends on CONFIG_IP_PNP.

I can't work out why it's not being set.

Any help appreciated,
Martin.

Looking at the build output I see the following lines are executed
/ws/rufilla/octopus/openwrt/scripts/package-metadata.pl kconfig /ws/rufilla/octopus/openwrt/tmp/.packageinfo /ws/rufilla/octopus/openwrt/.config 4.14 > /ws/rufilla/octopus/openwrt/build_dir/target-mipsel_24kc_musl/linux-ramips_mt76x8/linux-4.14.179/.config.override
/ws/rufilla/octopus/openwrt/scripts/kconfig.pl 'm+' '+' /ws/rufilla/octopus/openwrt/build_dir/target-mipsel_24kc_musl/linux-ramips_mt76x8/linux-4.14.179/.config.target /dev/null /ws/rufilla/octopus/openwrt/build_dir/target-mipsel_24kc_musl/linux-ramips_mt76x8/linux-4.14.179/.config.override > /ws/rufilla/octopus/openwrt/build_dir/target-mipsel_24kc_musl/linux-ramips_mt76x8/linux-4.14.179/.config.set

CONFIG_IP_PNP is not in .config.override
it is in .config.target, but it doesn't end up in .config.set even though

CONFIG_IP_PNP_DHCP=y

does, ie .config.set looks like this

# CONFIG_IP_PNP is not set
# CONFIG_IP_PNP_BOOTP is not set
CONFIG_IP_PNP_DHCP=y
# CONFIG_IP_PNP_RARP is not set

So I think this is where the problem is but I don't know what the package-metadata.pl and kconfig.pl scripts are trying to do.

-Martin