tests: stop comparing text addresses

on OS X, ntop produces strings like '3ffe:507::1:200:86ff:fe05:80da'
while others (NetBSD, Linux) produce '3ffe:507:0:1:200:86ff:fe05:80da'.

RFC 5952 4.2.2. says OS X behaviour is incorrect. (MUST NOT)
for longer term, it's probably better to workaround this in addrconv module.

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>