elf: Move la_activity (LA_ACT_ADD) after _dl_add_to_namespace_list() (BZ #28062)

It ensures that the the namespace is guaranteed to not be empty.

Checked on x86_64-linux-gnu.

Reviewed-by: Florian Weimer <fweimer@redhat.com>
(cherry picked from commit ed3ce71f)

Resolved conflicts:
	elf/Makefile