ospfd: Restore POINTOMULTIPOINT to working order

ospfd: Restore POINTOMULTIPOINT to working order

Commit: 1d376ff539508f336cb5872c5592b780e3db180b removed
the code to find nexthops for the POINTOMULTIPOINT and
replaced it with a generic bit of code that was
supposed to handle both POINTOPOINT and POINTOMULTIPOINT
the problem is that the ospf rfc states that the
network mask on point to multipoint should be /32
which will not allow you to properly do a prefix match
on it against the network.

Restore original behavior as much as possible and leave
the new POINTOPOINT code alone.

Fixes: #7624
Signed-off-by: Donald Sharp <sharpd@nvidia.com>