Fix AEAD parameter order / naming.

The order of parameters were in the wrong order. Make them equal
to the official order of libsodium.

While here, rename NONCEBYTES to NPUBBYTES so it reflects the
underlying names as well.

test/enacl_SUITE.erl

@@ -103,14 +103,15 @@ aead_xchacha20poly1305(_Config) ->
     ok.
 
 aead_chacha20poly1305(_Config) ->
+    NonceLen = enacl:aead_chacha20poly1305_NPUBBYTES(),
     KLen = enacl:aead_chacha20poly1305_KEYBYTES(),
     Key = binary:copy(<<"K">>, KLen),
     Msg = <<"test">>,
     AD = <<1,2,3,4,5,6>>,
-    Nonce = 1337,
+    Nonce = binary:copy(<<"N">>, NonceLen),
 
-    CipherText = enacl:aead_chacha20poly1305_encrypt(Key, Nonce, AD, Msg),
-    Msg = enacl:aead_chacha20poly1305_decrypt(Key, Nonce, AD, CipherText),
+    CipherText = enacl:aead_chacha20poly1305_encrypt(Msg, AD, Nonce, Key),
+    Msg = enacl:aead_chacha20poly1305_decrypt(CipherText, AD, Nonce, Key),
     ok.
 
 pwhash(_Config) ->