tcp: use semicolons rather than commas to separate statements

Replace commas with semicolons.  Commas introduce unnecessary
variability in the code structure and are hard to see.  What is done
is essentially described by the following Coccinelle semantic patch
(http://coccinelle.lip6.fr/):

// <smpl>
@@ expression e1,e2; @@
e1
-,
+;
e2
... when any
// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
Link: https://lore.kernel.org/r/1602412498-32025-4-git-send-email-Julia.Lawall@inria.fr
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/tcp_input.c

@@ -4430,7 +4430,8 @@ static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
 				sp[i] = sp[i + 1];
 			continue;
 		}
-		this_sack++, swalk++;
+		this_sack++;
+		swalk++;
 	}
 }