fix(session): make utility function names consistent

Before this commit behavior of `is_banned_msg/1` / `should_discard/1`
were actually the exact opposite of their names.

Co-Authored-By: Thales Macedo Garitezi <thalesmg@gmail.com>

apps/emqx/src/emqx_session.erl

@@ -92,7 +92,7 @@
 -export([enrich_delivers/3]).
 
 % Utilities
--export([should_discard/1]).
+-export([should_keep/1]).
 
 % Tests only
 -export([get_session_conf/2]).
@@ -497,12 +497,12 @@ on_dropped_qos2_msg(PacketId, Msg, RC) ->
 
 %%--------------------------------------------------------------------
 
--spec should_discard(message() | emqx_types:deliver()) -> boolean().
-should_discard(MsgDeliver) ->
-    is_banned_msg(MsgDeliver).
+-spec should_keep(message() | emqx_types:deliver()) -> boolean().
+should_keep(MsgDeliver) ->
+    not is_banned_msg(MsgDeliver).
 
 is_banned_msg(#message{from = ClientId}) ->
-    [] =:= emqx_banned:look_up({clientid, ClientId}).
+    [] =/= emqx_banned:look_up({clientid, ClientId}).
 
 %%--------------------------------------------------------------------
 

apps/emqx/src/emqx_session_mem.erl

@@ -211,10 +211,10 @@ open(ClientInfo = #{clientid := ClientId}, _ConnInfo) ->
     end.
 
 clean_session(ClientInfo, Session = #session{mqueue = Q}, Pendings) ->
-    Q1 = emqx_mqueue:filter(fun emqx_session:should_discard/1, Q),
+    Q1 = emqx_mqueue:filter(fun emqx_session:should_keep/1, Q),
     Session1 = Session#session{mqueue = Q1},
     Pendings1 = emqx_session:enrich_delivers(ClientInfo, Pendings, Session),
-    Pendings2 = lists:filter(fun emqx_session:should_discard/1, Pendings1),
+    Pendings2 = lists:filter(fun emqx_session:should_keep/1, Pendings1),
     {true, Session1, Pendings2}.
 
 %%--------------------------------------------------------------------