elf: Ignore LD_AUDIT interfaces if la_version returns 0 [BZ #24122]

This change moves the audit module loading and early notification into
separate functions out of dl_main.

It restores the bug fix from commit
8e889c5d  ("elf: Fix LD_AUDIT for
modules with invalid version (BZ#24122)") which was reverted in commit
83e6b596  ("[elf] Revert 8e889c5d
(BZ#24122)").

The actual bug fix is the separate error message for the case when
la_version returns zero.  The dynamic linker error message (which is
NULL in this case) is no longer used.  Based on the intended use of
version zero (ignore this module due to explicit request), the message
is only printed if debugging is enabled.