In this commit, the `MigrateGraphToSQL` function is expanded to migrate
the channel and channe policy data. Both of these have the special case
where the kvdb store records may contain invalid TLV. If we encounter a
channel with invalid TLV, we skip it and its policies. If we encounter a
policy with invalid TLV, we skip it.
The `TestMigrateGraphToSQL` and `TestMigrationWithChannelDB` tests are
updated accordingly.