dccp: snoop, build system fixes

@@ -236,10 +236,12 @@
 extern int interpret_udp(int, struct udphdr *, int, int);
 extern int interpret_esp(int, uint8_t *, int, int);
 extern int interpret_ah(int, uint8_t *, int, int);
 struct sctp_hdr;
 extern void interpret_sctp(int, struct sctp_hdr *, int, int);
+struct dccphdr;
+extern int interpret_dccp(int, struct dccphdr *, int, int);
 extern void interpret_mip_cntrlmsg(int, uchar_t *, int);
 struct dhcp;
 extern int interpret_dhcp(int, struct dhcp *, int);
 extern int interpret_dhcpv6(int, const uint8_t *, int);
 struct tftphdr;