This surname is common in Western Greece (area of Aitolia-Akarnania).
I don't think that it has anything to do with "garlic". Garlic is "skordo" in Greek (in that case the name should be "Skordas").
I think that it is of Albanian origin like many names in modern Greece. (Albanians settled in the Greek peninsula during the Byzantine and Ottoman period and they, gradually, assimilated with the local populations.)
There is a lake S(h)kodra in Albania, so the name could mean a person coming from that area.