fix: gas: estimate gas with a zero base-fee

Otherwise, an account will need funds to estimate the max possible gas a
message could take (which is usually the block gas limit).

This does mean gas estimation no longer checks if the sending account
has enough funds to cover the message cost, but MpoolPush will now do
this.

node/impl/full/gas.go

@@ -258,8 +258,8 @@ func gasEstimateGasLimit(
 ) (int64, error) {
 	msg := *msgIn
 	msg.GasLimit = build.BlockGasLimit
-	msg.GasFeeCap = types.NewInt(uint64(build.MinimumBaseFee) + 1)
-	msg.GasPremium = types.NewInt(1)
+	msg.GasFeeCap = big.Zero()
+	msg.GasPremium = big.Zero()
 
 	fromA, err := smgr.ResolveToKeyAddress(ctx, msgIn.From, currTs)
 	if err != nil {

node/impl/full/mpool.go

@@ -9,6 +9,7 @@ import (
 	"golang.org/x/xerrors"
 
 	"github.com/filecoin-project/go-address"
+	"github.com/filecoin-project/go-state-types/big"
 
 	"github.com/filecoin-project/lotus/api"
 	"github.com/filecoin-project/lotus/chain/messagepool"
@@ -178,8 +179,9 @@ func (a *MpoolAPI) MpoolPushMessage(ctx context.Context, msg *types.Message, spe
 		return nil, xerrors.Errorf("mpool push: getting origin balance: %w", err)
 	}
 
-	if b.LessThan(msg.Value) {
-		return nil, xerrors.Errorf("mpool push: not enough funds: %s < %s", b, msg.Value)
+	requiredFunds := big.Add(msg.Value, msg.RequiredFunds())
+	if b.LessThan(requiredFunds) {
+		return nil, xerrors.Errorf("mpool push: not enough funds: %s < %s", b, requiredFunds)
 	}
 
 	// Sign and push the message