Which config option is responsible for inclusion of arp?

 I copied AMIGA to KERNEL, and modified it to get the same set of options
 I had in 1.5. Compile then failed with a couple of unresolved symbols which
 I was able to locate in netinet/if_arp. Adding netinet/if_arp.[co] to the
 Makefile manually solved this problem, but I shouldn't have to do this (the
 resulting kernel works fine :).

 The only new option in my 1.5.1 config file is pseudo-device  vlan,
 but the errors come from net/if_ethersubr.c, IIRC.