cmd/utils, eth: init etherbase from within eth (#15528)

eth/backend.go

@@ -310,10 +310,17 @@ func (s *Ethereum) Etherbase() (eb common.Address, err error) {
 	}
 	if wallets := s.AccountManager().Wallets(); len(wallets) > 0 {
 		if accounts := wallets[0].Accounts(); len(accounts) > 0 {
-			return accounts[0].Address, nil
+			etherbase := accounts[0].Address
+
+			s.lock.Lock()
+			s.etherbase = etherbase
+			s.lock.Unlock()
+
+			log.Info("Etherbase automatically configured", "address", etherbase)
+			return etherbase, nil
 		}
 	}
-	return common.Address{}, fmt.Errorf("etherbase address must be explicitly specified")
+	return common.Address{}, fmt.Errorf("etherbase must be explicitly specified")
 }
 
 // set in js console via admin interface or wrapper from cli flags