Bug-1953: Fix bgpcep tests

-ipv4/6 prefixes must contain mask

Change-Id: I93c4ce30e98f5a0cd5fa8ba86a39129ee837d800
Signed-off-by: Milos Fabian <milfabia@cisco.com>
(cherry picked from commit 1dcca9cd957ec7a0ea17765b58cf07db12e0f251)