Tcp: fixed TcpHeader parsim/unparsim (issue #961)

Verified with next code in Tcp::handleLowerPacket():

{
    cCommBuffer *b = check_and_cast<cCommBuffer *>(createOne("omnetpp::cMemCommBuffer"));
    tcpHeader.get()->parsimPack(b);
    auto h = makeShared<TcpHeader>();
    h->parsimUnpack(b);
    ASSERT(h->getChunkLength() == tcpHeader->getChunkLength());
    ASSERT(h->getHeaderOptionArrayLength() == tcpHeader->getHeaderOptionArrayLength());
    MemoryOutputStream s1, s2;
    Chunk::serialize(s1, tcpHeader);
    Chunk::serialize(s2, h);
    ASSERT(s1.getData() == s2.getData());
}

src/inet/transportlayer/tcp_common/TcpHeader.msg

@@ -225,6 +225,19 @@ class TcpHeader extends TransportHeaderBase
     TcpOption *headerOption[] @owned;
 }
 
+cplusplus(cc) {{
+void doParsimPacking(omnetpp::cCommBuffer *b, TcpOption *t)
+{
+    b->packObject(t);
+}
+
+void doParsimUnpacking(omnetpp::cCommBuffer *b, TcpOption * &t)
+{
+    t = check_and_cast<TcpOption*>(b->unpackObject());
+}
+
+}}
+
 cplusplus(TcpHeader) {{
   public:
     /**