WIP: XX-3782 / Fix slow file transfer

cmd/fileTransfer.go

fileTransfer/manager.go

fileTransfer/oldTransferRecovery.go

fileTransfer/receive.go

fileTransfer/send.go

fileTransfer/sendNew.go

fileTransfer/send_test.go

fileTransfer/sentRoundTracker.go

go.mod

go.sum

network/gateway/hostPool.go

network/manager.go

network/message/manager.go

network/message/sendCmix.go

network/message/sendManyCmix.go