[U-Boot] [PATCH 3/5] configs: stm32f469-discovery: Disable CONFIG_NET flag

[Patrick DELAUNAY]

> 
> Network support was never added on this board, disable CONFIG_NET flag to
> avoid following warning:
> 
> ===================== WARNING ====================== This board
> does not use CONFIG_DM_ETH (Driver Model for Ethernet drivers). Please update
> the board to use CONFIG_DM_ETH before the v2020.07 release. Failure to
> update by the deadline may result in board removal.
> See doc/driver-model/migration.rst for more info.
> ====================================================
> 
> Signed-off-by: Patrice Chotard <patrice.chotard at st.com>
> ---

Applied to u-boot-stm32/master, thanks!