Add MPP option in payment settings

[Darth-Coin]

Describe your enhancement idea

We have MPP switch into payment modal that have to be activated manually each time before making the payment. What about adding a general option in Settings - "Payment settings" ? And put a condition:

• if the user have only 1 channel, the option cannot be activated (to avoid other possible issues)
• if the user have 2 or more channels, can activate MPP by default to all payments.

The MPP still can be enabled/disabled in each payment manually as user wish.

[kaloudis]

What's the problem with having mpp enabled when you have just one channel?

[Darth-Coin]

I had some problems sending a payment with MPP activated in Blixt, having just 1 channel. I think was something related to how LND is splitting in some fix shards. Can't remember exactly, but Hampus fix it with adding some code. With 2 or more there's no problem, payment went smooth, using both channels.