Try this patch:
diff -X dontdiff.ny -urNp linux-2.6.11-rc2.orig/include/linux/netfilter_ipv4/ip_conntrack_tftp.h linux-2.6.11-rc2/include/linux/netfilter_ipv4/ip_conntrack_tftp.h
--- linux-2.6.11-rc2.orig/include/linux/netfilter_ipv4/ip_conntrack_tftp.h 2005-01-22 15:23:45.000000000 +0100
+++ linux-2.6.11-rc2/include/linux/netfilter_ipv4/ip_conntrack_tftp.h 2005-01-23 01:31:25.000000000 +0100
@@ -13,7 +13,7 @@ struct tftphdr {
#define TFTP_OPCODE_ACK 4
#define TFTP_OPCODE_ERROR 5
-unsigned int (*ip_nat_tftp_hook)(struct sk_buff **pskb,
+extern unsigned int (*ip_nat_tftp_hook)(struct sk_buff **pskb,
enum ip_conntrack_info ctinfo,
struct ip_conntrack_expect *exp);