lnd: Call loader.UnloadWallet on shutdown

This is required to make restart work for LndMobile builds.
Not calling UnloadWallet would make `UnlockWallet` stall forever as
the file is already opened.

lnd.go

@@ -387,6 +387,11 @@ func Main(cfg *Config, lisCfg ListenerCfg, shutdownChan <-chan struct{}) error {
 		walletInitParams = *params
 		privateWalletPw = walletInitParams.Password
 		publicWalletPw = walletInitParams.Password
+		defer func() {
+			if err := walletInitParams.UnloadWallet(); err != nil {
+				ltndLog.Errorf("Could not unload wallet: %v", err)
+			}
+		}()
 
 		if walletInitParams.RecoveryWindow > 0 {
 			ltndLog.Infof("Wallet recovery mode enabled with "+
@@ -944,6 +949,10 @@ type WalletUnlockParams struct {
 	// ChansToRestore a set of static channel backups that should be
 	// restored before the main server instance starts up.
 	ChansToRestore walletunlocker.ChannelsToRecover
+
+	// UnloadWallet is a function for unloading the wallet, which should
+	// be called on shutdown.
+	UnloadWallet func() error
 }
 
 // waitForWalletPassword will spin up gRPC and REST endpoints for the
@@ -1105,6 +1114,7 @@ func waitForWalletPassword(cfg *Config, restEndpoints []net.Addr,
 			RecoveryWindow: recoveryWindow,
 			Wallet:         newWallet,
 			ChansToRestore: initMsg.ChanBackups,
+			UnloadWallet:   loader.UnloadWallet,
 		}, nil
 
 	// The wallet has already been created in the past, and is simply being
@@ -1115,6 +1125,7 @@ func waitForWalletPassword(cfg *Config, restEndpoints []net.Addr,
 			RecoveryWindow: unlockMsg.RecoveryWindow,
 			Wallet:         unlockMsg.Wallet,
 			ChansToRestore: unlockMsg.ChanBackups,
+			UnloadWallet:   unlockMsg.UnloadWallet,
 		}, nil
 
 	case <-signal.ShutdownChannel():

walletunlocker/service.go

@@ -81,6 +81,10 @@ type WalletUnlockMsg struct {
 	// ChanBackups a set of static channel backups that should be received
 	// after the wallet has been unlocked.
 	ChanBackups ChannelsToRecover
+
+	// UnloadWallet is a function for unloading the wallet, which should
+	// be called on shutdown.
+	UnloadWallet func() error
 }
 
 // UnlockerService implements the WalletUnlocker service used to provide lnd
@@ -346,6 +350,7 @@ func (u *UnlockerService) UnlockWallet(ctx context.Context,
 		Passphrase:     password,
 		RecoveryWindow: recoveryWindow,
 		Wallet:         unlockedWallet,
+		UnloadWallet:   loader.UnloadWallet,
 	}
 
 	// Before we return the unlock payload, we'll check if we can extract