xftp: add quota param to server CLI, restrict chunk sizes (#659)

* xftp: add quota param to server CLI

* only allow certain file sizes, fix tests

src/Simplex/FileTransfer/Client/Main.hs

@@ -52,7 +52,7 @@ xftpClientVersion :: String
 xftpClientVersion = "0.1.0"
 
 defaultChunkSize :: Word32
-defaultChunkSize = 8 * mb
+defaultChunkSize = 4 * mb
 
 smallChunkSize :: Word32
 smallChunkSize = 1 * mb
@@ -63,9 +63,6 @@ fileSizeLen = 8
 authTagSize :: Int64
 authTagSize = fromIntegral C.authTagSize
 
-mb :: Num a => a
-mb = 1024 * 1024
-
 newtype CLIError = CLIError String
   deriving (Eq, Show, Exception)