Don't print 'neighbor activate' if its default for IPv4 unicast AFI/SAFI

Don't print 'neighbor activate' if its default for IPv4 unicast AFI/SAFI

Ticket: CM-11460
Reviewed By: CCR-4927
Testing Done:

Quagga's default "show running" model is to only print the non-default config.
Historically, IPv4 unicast has always had a default 'activate' model unless
its been configured otherwise. In 3.0, we introduced a print of the 'activate'
statement for IPv4 unicast independent of whether it was the default or not.
This causes quagga reload to break as the user doesn't configure 'activate' for
IPv4 unicast, and so any config changes will also not have it. However 'show
running' will display it, causing quagga reload to think that the AFI/SAFI has
been deactivated and bounce the sessions incorrectly.

This patch reverts to the original quagga behavior/model of not printing the
'activate' line for IPv4 unicast if its the default.