message: Add tcp_packet_iter function.
diff: @@ -28,6 +28,7 @@ use packet::ip::IpNextHeaderProtocol;
  use packet::ipv4::Ipv4Packet;
  use packet::udp::UdpPacket;
  use packet::icmp::IcmpPacket;
  +use packet::tcp::TcpPacket;
  use self::TransportChannelType::{Layer3, Layer4};
  use self::TransportProtocol::{Ipv4, Ipv6};
  use sockets;
  @@ -292,3 +293,6 @@ transport_channel_iterator!(Ipv4Packet, Ipv4TransportChannelIterator, ipv4_packe
  transport_channel_iterator!(UdpPacket, UdpTransportChannelIterator, udp_packet_iter);
  transport_channel_iterator!(IcmpPacket, IcmpTransportChannelIterator, icmp_packet_iter);
  +
  +transport_channel_iterator!(TcpPacket, TcpTransportChannelIterator, tcp_packet_iter);
  +
  