kernel: modules: add boot flag to igc, mlx4, and mlx5 drivers

kernel: modules: add boot flag to igc, mlx4, and mlx5 drivers

Set the boot flag for the igc, mlx4-core, and mlx5-core network device drivers
to load them at a more early stage of the boot process.

This is required for network drivers whose network interface PCI paths are set
via ucidef_set_network_device_path inside the 02_network script since it is
called after kernel modules are loaded from modules-boot.d but before they are
loaded from the modules.d directory.

Signed-off-by: Til Kaiser <mail@tk154.de>
Link: https://github.com/openwrt/openwrt/pull/16560
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>