cmd: net: fix function name in comment

In commit 7044c6bb (net: cosmetic: Clean up DHCP variables and functions)
BootpCopyNetParams() was renamed to store_net_params(). Update the reference in
comment.

Cc: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>