Renegotiate the connection by starting a new handshake. Note that
the accept callback will be called again when the handshake is
finished.
Returns zero if there are any I/O errors. errno() will give the
details.
Note
The read buffer is not cleared - a read() afterwards will
return data from both before and after the renegotiation.
Bugs
Data in the write queue in nonblocking mode is not properly
written before resetting the connection. Do a blocking
write("") first to avoid problems with that.