[ln] Prevent using with SPV (#2307)
[ln] Prevent using with SPV (#2307)

dcrlnd does not currently support SPV mode so we need to disable the ability
to use LN when the wallet is configured as SPV.
decred/decrediton,decred/decrediton,decred/decrediton,decred/decrediton,decred/decrediton,decred/decrediton