dbft: skip extensible verification if node is syncing

Nodes (both miners and seeds) can't properly validate consensus payloads
if they are syncing. This check prevents both type of nodes from
consensus payloads validation if the node is in the process of the
initial sync. Next possible Downloader activity is not taken into
account.

Close #296.

Signed-off-by: Anna Shaleva <[email protected]>

Author: AnnaShaleva

consensus/dbft/dbft.go

@@ -1518,6 +1518,10 @@ func (c *DBFT) validatePayload(p *Payload) error {
 // IsExtensibleAllowed determines if address is allowed to send extensible payloads
 // (only consensus payloads for now) at the specified height.
 func (c *DBFT) IsExtensibleAllowed(h uint64, u common.Address) bool {
+	// Can't verify extensible sender if the node has an outdated state.
+	if c.syncing.Load() {
+		return true
+	}
 	// Only validators are included into extensible whitelist for now.
 	validators, err := c.getValidators(&h, nil, nil)
 	if err != nil {