iphlpapi: Include netinet/if_inarp.h for NetBSD.
diff --git a/configure.ac b/configure.ac
index 1a2828d..66ad0ac 100644
--- a/configure.ac
+++ b/configure.ac
@@ -386,6 +386,7 @@
 	net/if_types.h \
 	net/route.h \
 	netinet/if_ether.h \
+	netinet/if_inarp.h \
 	netinet/in_pcb.h \
 	netinet/ip_icmp.h \
 	netinet/ip_var.h \