multi: fix linter issues

This commit fixes outstanding linter issues, that we're not found by
running `make lint` locally. The linter issues were found by running
`docker run -v $(pwd):/build loop-tools golangci-lint run --whole-files`

I added the `revive` to the excludes as it would be to much of a
refactor and IMO seems unneccesary. E.g.
`interface.go:222:6: exported: type name will be used as
loop.LoopInTerms by other packages, and that stutters; consider
 calling this InTerms (revive)`. I think `loop.LoopInTerms` is fine.

loopdb/loop.go

@@ -58,7 +58,7 @@ type SwapContract struct {
 	ProtocolVersion ProtocolVersion
 }
 
-// Loop contains fields shared between LoopIn and LoopOut
+// Loop contains fields shared between LoopIn and LoopOut.
 type Loop struct {
 	Hash   lntypes.Hash
 	Events []*LoopEvent

loopdb/meta.go

@@ -92,7 +92,6 @@ func syncVersions(db *bbolt.DB, chainParams *chaincfg.Params) error {
 		"db_version=%v", latestDBVersion, currentVersion)
 
 	switch {
-
 	// If the database reports a higher version that we are aware of, the
 	// user is probably trying to revert to a prior version of lnd. We fail
 	// here to prevent reversions and unintended corruption.