Update UdpEchoClientApplication to comply with ns-3 v3.45

[dpugliese6]

Starting v3.45 of ns-3, RemoteAddress and RemotePort attributes have been replaced by an AddressValue object. IoD_Sim applications, and in particular UdpEchoClientApplication, must be adapted accordingly. The scenario configuration helper already parse the new JSON parameter Attribute following @domysh LENA integration.

[dpugliese6]

UdpEchoClientApplication extend the functionalities of the native class UdpEchoClient (which is compliant with the new address definition standard) adding a sequence number on UDP packets for debug purposes

Code snippet from @GiovanniGrieco:
SeqTsHeader seqTs;
seqTs.SetSeq(m_sent);
Ptr p = Create(m_size - 8 + 4); // 8+4 : the size of the seqTs header
p->AddHeader(seqTs);