escl: Fix ipv6 detection.
Avahi sometimes makes an error on IPV4/IPV6 type detection. Check if IPV6 is active on the SANE project and verify that we have an IPV6 type address.
xxxxxx@yyyyyyyyy:~$ scanimage -L
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device `escl:https://[192.168.0.177]:443' is a Canon S6300 auto platen scanner
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xxxxxx@yyyyyyyyy:~$