tests: Add a bit less and slightly smaller sections for addsections

tests: Add a bit less and slightly smaller sections for addsections

The run-copymany-sections.sh testcase adds 64K sections (twice)
to a couple of times. Each section is just 6 bytes long, but each
data section is malloced and freed. That adds up. And is especially
slow when running under valgrind.

Reduce the number of sections added to 32K (twice) and make each
section data just one single zero byte.

	* tests/addsections.c (add_sections): Don't strdup and free
	the string ".extra", but just add the empty string.
	* tests/run-copymany-sections.sh: Call addsections with
	32768 instead of 65535.

Signed-off-by: Mark Wielaard <mark@klomp.org>