sweep: update BudgetInputSet.Budget() to factor in extra budget

In this commit, we update the `Budget()` call to factor in the
`extraBudget` value. Otherwise, when we go to intialize the fee
function, we won't factor in the extra budget, and will determine that
we can't broadcast/bump.

sweep/tx_input_set.go

@@ -373,7 +373,9 @@ func (b *BudgetInputSet) Budget() btcutil.Amount {
 		budget += input.params.Budget
 	}
 
-	return budget
+	// We'll also tack on the extra budget which will eventually be
+	// accounted for by the wallet txns when we're broadcasting.
+	return budget + b.extraBudget
 }
 
 // DeadlineHeight returns the deadline height of the set.