[SR-Users] str2ip6 bug is also in 3.3.3

[Juha Heinanen]

i tried to compile latest 3.3 and found that it failed to compile due to
same str2ip6 bug that was fixed in 4.0:

dns_cache.c: In function ���dns_cache_do_request���:
dns_cache.c:1894: warning: implicit declaration of function ���str2ip6���

-- juha