fix locked balance as fee

[zqhxuyuan]

Current, we use free balance which containts locked part to decide whether the user have enough native asset. If user locked most of native asset, and left transferable native asset less than ED. then withdraw those native asset will failed. Also, this would't use other token as fee payment. because current we either choose native asset if native asset is enough(in this case it's true) or other token if native asset is not enough.

Acala/modules/transaction-payment/src/lib.rs

Lines 765 to 766 in 11d9541

	if fee.saturating_add(native_existential_deposit) <= total_native {
	None