net: cosmetic: Change IPaddr_t to struct in_addr

This patch is simply clean-up to make the IPv4 type that is used match
what Linux uses. It also attempts to move all variables that are IP
addresses use good naming instead of CamelCase. No functional change.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Acked-by: Simon Glass <sjg@chromium.org>