tools/libvchan: notify server when client is connected

tools/libvchan: notify server when client is connected

Let the server know when the client is connected. Otherwise server will
notice only when client send some data.
This change does not break existing clients, as libvchan user should
handle spurious notifications anyway (for example acknowledge of remote
side reading the data).

Cc: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Replace spaces with tabs to match the file's whitespace.
Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>