modules: felix: Remove etherswitch_if.c from Makefile

Having it included confuses KOBJOPLOOKUP resulting in kobj_error_method
being called instead of a devmethod from the switch driver.
That in turn returns ENXIO which was treated as a pointer and
dereferenced by etherswitch ioctl logic causing the kernel to panic.

Fixes: b542c9e42ba4 (modules: felix: Add needed dependencies)