ospfd: fix NSSA translate-always

ospfd: fix NSSA translate-always

When an ABR NSSA router is configured to be ALWAYS the translator:
  r22(config-router)# area 1 nssa translate-always

It will advertise this condition in the type-1 LSA setting the Nt
bit, taking over the translator role from r33

  r22# show ip ospf
     We are an ABR and always an NSSA Translator.
  r33# show ip ospf
     We are an ABR, but not the NSSA Elected Translator.

However when the command above is removed:
  r22(config-router)# no area 1 nssa translate-always

the bit Nt needs to be cleared otherwise we end up with no translator
in the area
  r22# show ip ospf
     We are an ABR, but not the NSSA Elected Translator.
  r33# show ip ospf
     We are an ABR, but not the NSSA Elected Translator.

This PR forces the ABR to send a type-1 LSA with the Nt bit updated
according to the translator role

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