Workaround NBitcoin txout shuffling bug

NBitcoin's TransactionBuilder.ShuffleOutputs flag is broken and gets
ignored when building the Transaction. This can be worked around by
setting the TransactionBuilder's RandomShuffle field to null, which
disables all random shuffling.

This fix can be removed once NBitcoin bug #931 is fixed:

See:
MetacoSA/NBitcoin#931

src/DotNetLightning.Core/Transactions/Transactions.fs

@@ -302,6 +302,7 @@ module Transactions =
         let txb = network.CreateTransactionBuilder()
         txb.ShuffleOutputs <- false
         txb.ShuffleInputs <- false
+        txb.ShuffleRandom <- null
         txb
 
     let UINT32_MAX = 0xffffffffu