package/belle-sip: add BELLE_SIP_CPE_ID_VENDOR

cpe:2.3:a:linphone:belle-sip is a valid CPE identifier for this package:

  https://nvd.nist.gov/products/cpe/search/results?namingFormat=2.3&keyword=cpe%3A2.3%3Aa%3Alinphone%3Abelle-sip



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>