kernel: fix dependency chain of kmod-igb

The igb kmods selects kmod-i2c-algo-bit which in turn is invisible until
kmod-i2c-core gets selected, causing kmod-igb to be hidden from menuconfig
as well.

Let kmod-igb select kmod-i2c-core as well in order to make it visible
in menuconfig right away.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>