uboot-imx

net: remove CONFIG_NET_MULTI

This macro is defined, but not referenced by anyone.

I did not touch config_whitelist.txt - the CONFIG will be dropped
by the next re-sync.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: York Sun <york.sun@nxp.com>