Improve reload behaviour of RDE peer flags and export_type.

Improve reload behaviour of RDE peer flags and export_type.

Add an extra reload barrier (IMSG_RECONF_DRAIN) to the sync of the peer
config from the session engine to the rde. Necessary to ensure that the
peer config is up to date in the RDE before hitting reconfiguration.

Store the export_type and the peer flags outside of peer->conf. Adjust all
users of these two fields so they only look at the copies in peer.
During reload check the values with the peer->conf to check for changes.

If the export_type or the rde evaluate or transparent-as flags changed
flush the Adj-RIB-Out for that peer and in a 2nd step rebuild the RIB from
scratch. This results in a lot of UPDATE churn but these configs are not
altered often.

Fix multiple issues in the rde_softreconfig_in_done handler that resulted
in multiple runs of the out stage of the softreconfig pipeline.

OK benno@