Fix a comment in WalSnd structure

Hi,

WalSnd structure mutex is being used to protect all the variables of
that structure, not just 'variables shown above' [1]. A tiny patch
attached to fix the comment.

Thoughts?

[1]
diff --git a/src/include/replication/walsender_private.h
b/src/include/replication/walsender_private.h
index c14888e493..9c61f92c44 100644
--- a/src/include/replication/walsender_private.h
+++ b/src/include/replication/walsender_private.h
@@ -65,7 +65,7 @@ typedef struct WalSnd
         */
        int                     sync_standby_priority;

-       /* Protects shared variables shown above. */
+       /* Protects shared variables in this structure. */
        slock_t         mutex;

--
Bharath Rupireddy
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