MAINTAINERS: add Kuniyuki Iwashima to TCP reviewers

List Kuniyuki as an official TCP reviewer.

Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250202014728.1005003-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

MAINTAINERS

@@ -16614,6 +16614,7 @@ F:	tools/testing/selftests/net/mptcp/
 NETWORKING [TCP]
 M:	Eric Dumazet <edumazet@google.com>
 M:	Neal Cardwell <ncardwell@google.com>
+R:	Kuniyuki Iwashima <kuniyu@amazon.com>
 L:	netdev@vger.kernel.org
 S:	Maintained
 F:	Documentation/networking/net_cachelines/tcp_sock.rst