NAT_TCP
#define NAT_TCPUDP (NAT_TCP|NAT_UDP)
#define NAT_TCPUDPICMP (NAT_TCP|NAT_UDP|NAT_ICMPERR)
#define NAT_TCPUDPICMPQ (NAT_TCP|NAT_UDP|NAT_ICMPQUERY)
#define NAT_FROMRULE (NAT_TCP|NAT_UDP)
nflags = NAT_TCP;