MAINTAINERS: add Neal to TCP maintainers

Neal Cardwell has been indispensable in TCP reviews
and investigations, especially protocol-related.
Neal is also the author of packetdrill.

Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250129191332.2526140-1-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>