Add SPDX license (but not copyright) headers to all files which follow a
certain pattern in their existing non-machine-readable header comment.
This commit was entirely generated using the command:
```
git ls-files gio/*.[ch] | xargs perl -0777 -pi -e 's/\n \*\n \* This library is free software; you can redistribute it and\/or\n \* modify it under the terms of the GNU Lesser General Public/\n \*\n \* SPDX-License-Identifier: LGPL-2.1-or-later\n \*\n \* This library is free software; you can redistribute it and\/or\n \* modify it under the terms of the GNU Lesser General Public/igs'
```
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Helps: #1415
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.
Add a new GDtlsConnection interface, plus derived GDtlsClientConnection
and GDtlsServerConnection interfaces, for implementing Datagram TLS
support in glib-networking.
A GDtlsConnection is a GDatagramBased, so may be used as a normal
datagram socket, wrapping all datagrams from a base GDatagramBased in
DTLS segments.
Test cases are included in the implementation in glib-networking.
https://bugzilla.gnome.org/show_bug.cgi?id=752240
