You have to figure out where is the kernel config.
It may be compiled into kernel as /proc/config.gz. In this case:
zcat /proc/config.gz |grep AX25
Usually sarge has /boot/config... to store configuration:
grep AX25 /boot/config-2.6.7-xtops5
I am not completely sure if AX25 kernel config options is exactly what you mean.