KLD is preloaded with loader(8) and leads to infinity loops.
Also do not return EEXIST error code from MOD_LOAD handler, because
we have undocumented(?) ability replace kernel's module with preloaded one.
And if we have so, then preloaded module will be initialized first.
Thus error in MOD_LOAD handler will be triggered for the kernel.
PR: kern/165573
MFC after: 3 weeks