elf: Add _dl_audit_activity_map and _dl_audit_activity_nsid

It consolidates the code required to call la_activity audit
callback.

Also for a new Lmid_t the namespace link_map list are empty, so it
requires to check if before using it.  This can happen for when audit
module is used along with dlmopen.

Checked on x86_64-linux-gnu, i686-linux-gnu, and aarch64-linux-gnu.

Reviewed-by: Florian Weimer <fweimer@redhat.com>
(cherry picked from commit 3dac3959)