MAINTAINERS: Stephen Hemminger email change

[ Upstream commit adbbf69d1a54abf424e91875746a610dcc80017d ]

I changed my email because the vyatta.com mail server is now
redirected to brocade.com; and the Brocade mail system
is not friendly to Linux desktop users.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>