config: Initialize Graceful Restart State
config: Initialize Graceful Restart State

Currently, the restarting speaker ends restarting procedure
before receiving End-of-Rib markers from all helper speakers.
It is because `MpGracefulRestart.State.Enabled` is not initialized,
always evalueted to false, so the restarting speaker misunderstands
as there is not helper speaker.

This patch adds code to initialize `MpGracefulRestart.State.Enabled`.
This fixes #1296.

Signed-off-by: Satoshi Fujimoto <cd75558e8cccb245feb2368a5a53f09e4ecc2257@gmail.com>

a16/gobgp,fujita/gobgp,a16/gobgp,a16/gobgp,a16/gobgp,osrg/gobgp,a16/gobgp,fujita/gobgp,a16/gobgp,j-kato/gobgp,ishidawataru/gobgp,tamihiro/gobgp,Dipsingh/gobgp,tamihiro/gobgp,Dipsingh/gobgp,a16/gobgp,ishidawataru/gobgp,Dipsingh/gobgp,osrg/gobgp,tamihiro/gobgp,osrg/gobgp,tamihiro/gobgp,fujita/gobgp,j-kato/gobgp,ishidawataru/gobgp,j-kato/gobgp,fujita/gobgp,osrg/gobgp