janus-gateway: rename options to have proper prefix
The sub-options of the janus-gateway package had their name option
prefixed by BR2_PACKAGE_JANUS, while the prefix should be
BR2_PACKAGE_JANUS_GATEWAY. This commit fixes that, and adds the
necessary Config.in.legacy handling.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com> Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr> Signed-off-by: Peter Korsgaard <peter@korsgaard.com>