fix: revert to ChannelSet addSettings method without index

fixes throwing Non-fatal Exception: java.lang.IndexOutOfBoundsException: Index: N, Size: n

app/src/main/java/com/geeksville/mesh/repository/datastore/ChannelSetRepository.kt

@@ -53,7 +53,7 @@ class ChannelSetRepository @Inject constructor(
                     preference.toBuilder().setSettings(channel.index, channel.settings).build()
                 }
             } else {
-                preference.toBuilder().addSettings(channel.index, channel.settings).build()
+                preference.toBuilder().addSettings(channel.settings).build()
             }
         }
         return getAdminChannel()