ospfd: fix NSSA translator

ospfd: fix NSSA translator

Having 2 ABR in NSSA area where R3 is the elected translator

R3# show ip ospf
  We are an ABR and the NSSA Elected Translator.
R2# show ip ospf
  We are an ABR, but not the NSSA Elected Translator.

When R3 loses the Border condition by shutting down the interface
to the backbone, we end up with no translator in the NSSA area. It
is expected R2 to take over the translator role

R3# sh ip ospf
  It is not ABR, therefore not Translator.
R2# show ip ospf
   We are an ABR, but not the NSSA Elected Translator.

This PR forces the ABR to reevaluate the translator condition, so
R2 becomes the elected Translator

Signed-off-by: ckishimo <carles.kishimoto@gmail.com>