MAINTAINERS: add reviewers for SMC Sockets

adding three people from Alibaba as reviewers for SMC.
They are currently working on improving SMC on other architectures than
s390 and help with reviewing patches on top.

Thank you D. Wythe, Tony Lu and Wen Gu for your contributions and
collaboration and welcome on board as reviewers!

Reviewed-by: Wenjia Zhang <wenjia@linux.ibm.com>
Signed-off-by: Jan Karcher <jaka@linux.ibm.com>
Acked-by: Tony Lu <tonylu@linux.alibaba.com>
Acked-by: Wen Gu <guwen@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>