As a follow-up to r339930 (r339951 in stable/12) and various reports
implement logging in case we fail during module load because the pcpu
or vnet module sections are full.
We did return a proper error but not leaving any indication to the
user as to what the actual problem was.

Even worse, on 12/13 currently we are seeing an unrelated error (ENOSYS
instead of ENOSPC, which gets skipped over in kern_linker.c) to be
printed which made problem diagnostics even harder.