Add kmod-veth to BananaPi-R4 defconfig.

This enables the virtual Ethernet device kernel module for BananaPi-R4 builds.

BUG=b/514259535
TEST=./BPI-R4.sh

Change-Id: Ifc869ba34bcd9af34deb68c9cd0082da8cadb2d3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/7851292
Tested-by: Alexandr Astrouski <astrouski@google.com>
Reviewed-by: Jason Stanko <jstanko@google.com>
Commit-Queue: Alexandr Astrouski <astrouski@google.com>