CREDITS: Add entry for Shannon Nelson

I'm retiring and have already had my name removed from MAINTAINERS.
A couple of folks kindly suggested I should have an entry here.

Signed-off-by: Shannon Nelson <sln@onemain.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250619211607.1244217-1-sln@onemain.com


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