Linux compile error with 2.1.1

I've been running 2.0.0 for quite some time on a debian stable system 
without problems.  I just downloaded 2.1.1 to play with the embedded 
perl and I'm getting a compile error:

ife-sockpacket.c: In function `if_send_spoof_request':
ife-sockpacket.c:87: `ping_pkt' undeclared (first use in this function)
ife-sockpacket.c:87: (Each undeclared identifier is reported only once
ife-sockpacket.c:87: for each function it appears in.)

This happens on both debian stable with gcc 2.95.4 and gentoo with gcc 
3.3.4.  It looks like a missing declaration, but maybe I'm missing some 
library dependency?