[glib] gtlsbackend: Default to indicating no support for DTLS in GTlsBackend

[Philip Withnall <pwithnall src gnome org>]

commit 5e55a4e2439119f54cdd40030d5acc1f5714d9df
Author: Philip Withnall <withnall endlessm com>
Date:   Mon Sep 11 09:59:50 2017 +0100

    gtlsbackend: Default to indicating no support for DTLS in GTlsBackend
    
    I’m unsure what the original reasoning for returning TRUE by default
    from supports_dtls was, but it is not backwards-compatible. If a
    pre-existing GTlsBackend implementation never implements the
    supports_dtls vfunc, the supports_dtls() method will magically return
    TRUE rather than FALSE.
    
    Since any backend which does implement DTLS should be implementing the
    supports_dtls vfunc (and no DTLS-supporting backends have actually been
    merged yet; see bug #697908), it seems safer to make this slight API
    break in the name of backwards compatibility than to leave it as
    returning TRUE incorrectly.
    
    Signed-off-by: Philip Withnall <withnall endlessm com>
    
    https://bugzilla.gnome.org/show_bug.cgi?id=787485

 gio/gtlsbackend.c |    6 ++----
 1 files changed, 2 insertions(+), 4 deletions(-)
---
diff --git a/gio/gtlsbackend.c b/gio/gtlsbackend.c
index db156c8..80af6ad 100644
--- a/gio/gtlsbackend.c
+++ b/gio/gtlsbackend.c
@@ -143,10 +143,8 @@ g_tls_backend_supports_dtls (GTlsBackend *backend)
 {
   if (G_TLS_BACKEND_GET_INTERFACE (backend)->supports_dtls)
     return G_TLS_BACKEND_GET_INTERFACE (backend)->supports_dtls (backend);
-  else if (G_IS_DUMMY_TLS_BACKEND (backend))
-    return FALSE;
-  else
-    return TRUE;
+
+  return FALSE;
 }
 
 /**