HID: add mapping for "AL Network Chat" usage

Adding a mapping for the 'AL Network Chat' usage from the 'Consumer' usage
page (USB HID Usage Tables v1.11). This usage is used by some keyboards for
a multimedia key.

Signed-off-by: Leo P White <lpw25@cam.ac.uk>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>