ospf6d: Stop sending hello's out loopback interface

ospf6d: Stop sending hello's out loopback interface

Currently if you have this setup:

router ospf6
interface lo area 0.0.0.0

Ospf is scheduling and sending hello's out the loopback interface:
2016/03/18 15:26:12.463248 OSPF6: Could not send entire message
2016/03/18 15:26:22.463475 OSPF6: sendmsg failed: ifindex: 1: Network is unreachhable (101)

Adding a check to not schedule hello's for a loopback interface resolves this issue.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>
Reviewed-by: Don Slice <dslice@cumulusnetworks.com>