glib-networking: fix LICENSE statement

The glib-networking license is LGPLv2.1 _or later_ and also has an
additional exception if OpenSSL is being used.

Add source comments to the checksum, and extend LICENSE if the openssl
PACKAGECONFIG has been enabled.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>