zebra: send link parameters to zclients once they request interface info

zebra: send link parameters to zclients once they request interface info

We were sending ZEBRA_INTERFACE_LINK_PARAMS messages under the
following circumstances:
* New interface was created (via kernel or config);
* Interface went from down to up;
* Update in the link-params configuration.

Now also send ZEBRA_INTERFACE_LINK_PARAMS messages whenever a zclient
connects and sends a ZEBRA_INTERFACE_ADD request. Without this fix,
the client daemons don't receive interface link parameters if they
are configured in the zebra startup configuration.

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>