Previously we simply logged errors but never reported them to elements
or even to the user. Fatal errors are now properly reported.
Additionally proper connection closing is implemented based on EOS:
- dtlsenc: EOS will cause close_notify to be sent to the peer and only
if the peer also sent back close_notify we will forward the
EOS event.
- dtlsdec: EOS will be forwarded normally, this only means that the
unterlying transport was closed. On receiving a DTLS packet
containing close_notify, return EOS and send EOS downstream.
By passing NULL to `g_signal_new` instead of a marshaller, GLib will
actually internally optimize the signal (if the marshaller is available
in GLib itself) by also setting the valist marshaller. This makes the
signal emission a bit more performant than the regular marshalling,
which still needs to box into `GValue` and call libffi in case of a
generic marshaller.
Note that for custom marshallers, one would use
`g_signal_set_va_marshaller()` with the valist marshaller instead.
The agent itself will take a ref on the property setter, so we'll be
left with two references to the certificate object, when actually there
should be only one
By removing the indirection to the main loop completely when receiving
the peer certificate. For reference, the on-decoder-key signal does not
have a redirection.
