This commit uses the new SetBit helper for setting the Bolt11 route
blinding required bit in a generated invoice. This helper will take care
of setting the dependent bits of the feature bit (namely the route
blinding and TLV feature bits and will use the required variant of
both).
Prior to this commit, lnd could become unresponsive to shutdown signals
during the `IsSynced` check. Since the `IsSynced` check can occasionally
take a long time to complete, this could result in lnd failing to shut
down promptly.
