ospf6d: Make debug logs configurable to only display message headers

ospf6d: Make debug logs configurable to only display message headers

This change allows the user to only log the message header and not
include all the LSAs in each packet.   In a large setup printing out
all the LSAs in each packet can make the system very hard to debug.
When the user finds an issue with the adjacency not coming up or in a
specific packet type they can turn on a full dump of the message.

Signed-off-by: Lynne Morrison <lynne@voltanet.io>