Manage a connection to a SeedLink server based on the values
given in this SeedLinkConnection, and to collect data.
Designed to run in a tight loop at the heart of a client program, this
function will return every time a packet is received.
If the SeedLinkConnection was initialized with a timeout, the collect()
call will be terminated if it takes longer than self.timeout seconds
|Returns:||an SLPacket when something is received.
|Returns:||null when the connection was closed by
the server or the termination sequence completed.
| ||on error.