kernel: KERNEL_NET_L3_MASTER_DEV default to y if !SMALL_FLASH
Follow-up for 45d541bb40
This change allows features such as kmod-vrf
```
KERNEL_NET_L3_MASTER_DEV=n
x86_64 generic
bzImage 6,927,360 bytes
aarch64 coretex-a53
kernel 4,268,836 bytes
KERNEL_NET_L3_MASTER_DEV=y
x86_64 generic
bzImage 6,931,456 bytes
aarch64 coretex-a53
kernel 4,273,042 bytes
Delta:
x86_64 generic
+4096 bytes
aarch64 coretex-a53
+4206 bytes
x86_64 generic vrf.ko - 258,792 bytes
aarch64 coretex-a53 vrf.ko - 263,632 bytes
```
See:
https://forum.openwrt.org/t/vrf-support-testing-out-evpn-at-home/181108
https://forum.openwrt.org/t/please-enable-net-l3-master-dev-in-kernel-build-by-default/201825
Signed-off-by: Paul Donald <newtwen+github@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/16819
Signed-off-by: Robert Marko <robimarko@gmail.com>
2915cfb626