libelf: Always update e_version and e_shentsize in elf_update.

libelf: Always update e_version and e_shentsize in elf_update.

When e_version is EV_NONE we should set it to EV_CURRENT like we do for
the EI_VERSION and like we set EI_DATA to the correct byte order when set
to ELFDATANONE.  Likewise we should always set e_shentsize like we do for
e_phentsize, not just when ELF_F_LAYOUT isn't set.

Add a new elfshphehdr testcase to check the above.

Signed-off-by: Mark Wielaard <mjw@redhat.com>