* Enable virtual DNS by default.
* Improve handling of header size:
This fixes an issue in UDP, where it would not take the header size into account when deciding how much to read.
* IPRAW socket. Fix an issue where the header would include "our" IP Address.
The doc is not very clear 5.2.3: they say "destination". But for consistency with UDP (5.2.2) where it seems clear that this is the peer's ip, we replace with the "destination" of the socket, or the "source" of the packet.
* minor tweak: signal with SOCK_SYNSENT that a connection is being established.
* remove Socket::myErrno as it serves no purpose.
It is a duplicate of (sn_sr == W5100_SN_SR_SOCK_SYNSENT).
* add some logging when reading/writing on a closed socket.
