If we have an input parameter (or return value) we need to use (nullable).
However, if it is an (inout) or (out) parameter, (optional) is sufficient.
It looks like (nullable) could be used for everything according to the
Annotation documentation, but (optional) is more specific.
GDatagramBased allows connection-oriented and connection-less sockets,
but does not allow stream-based sockets (because it’s datagram-based).
So it supports SCTP and UDP, but not TCP.
Clarify that in the documentation, and people sometimes confuse
connection-oriented with stream-based, due to the prevalence of TCP.
GDatagramBased is an interface abstracting datagram-based communications
in the style of the Berkeley sockets API. It may be contrasted to (for
example) GIOStream, which supports only streaming I/O.
GDatagramBased allows socket-like communications to be done through any
object, not just a concrete GSocket (which wraps socket()).
This adds the GDatagramBased interface, and implements it in GSocket.
https://bugzilla.gnome.org/show_bug.cgi?id=697907
