MAINTAINERS: net: move Alexey Kuznetsov to CREDITS

Move Alexey to CREDITS.

I am probably not giving him enough justice with
the description line..

Subsystem NETWORKING [IPv4/IPv6]
  Changes 1535 / 5111 (30%)
  Last activity: 2020-12-10
  "David S. Miller" <davem@davemloft.net>:
    Author b7e4ba9a 2020-12-09 00:00:00 407
    Committer e0fecb28 2020-12-10 00:00:00 3992
    Tags e0fecb28 2020-12-10 00:00:00 3978
  Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>:
  Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>:
    Tags d5d8760b

 2016-06-16 00:00:00 8
  Top reviewers:
    [225]: edumazet@google.com
    [222]: dsahern@gmail.com
    [176]: ncardwell@google.com
  INACTIVE MAINTAINER Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>

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