Represent IPv6 addresses as groups of 16-bit values in test vectors.
This commit corrects the following two test issues on big endian
systems:
START - test_ipv6_pton_1
Failed to verify ff08::
against 0:ff08::
START - test_ipv6_ntop_1
Failed to verify 0:ff08::
against ff08::
Makes the following tests pass on qemu_leon3:
- net.util
Signed-off-by: Martin Åberg <martin.aberg@gaisler.com>