[0.8] Ignore google:jingleinfo pushes from contacts.
[0.8] Ignore google:jingleinfo pushes from contacts.

Previously, Gabble would erroneously process google:jingleinfo updates
sent by anybody, rather than only paying attention to those sent by the
user's server. This may theoretically allow an attacker to trick Gabble
into relaying streamed media through a server of the attacker's
choosing, enabling them to intercept, obstruct or modify the user's
audio and video calls.

This patch addresses this flaw, following the same pattern as the
corresponding check in the roster code.

Note that even without this flaw, no security guarantees on media in
calls can be provided in the presence of malicious network admins or
insecure networks: an attacker who can eavesdrop the network traffic
still has the ability to intercept the content of the call, as the media
is transmitted unencrypted.

Fixes: <https://bugs.freedesktop.org/show_bug.cgi?id=34048>
Signed-off-by: Will Thompson <5822fdda638242a44ccfa68f146ccf6f257c5cbd@collabora.co.uk>
Reviewed-by: Sjoerd Simons <1371fd10dd05a897e5b55dc6ae4fbafa1f84c6ec@collabora.co.uk>

community-ssu/telepathy-gabble,community-ssu/telepathy-gabble,community-ssu/telepathy-gabble,community-ssu/telepathy-gabble