'sallia' would appear to be related to be connected to the Irish word 'sáile', meaning 'salty'. e.g., the original name for Tacumshin LLake in Co. Wexford was @Lough Sale' in English, and 'Loch Sáile' in irish. Being a tombolo, it is partially, a salt-water lake.
I wonder does Weelia Wallia also come from Gaelic doggerl; was it originally sung in Irish/Gaelic? The Celtic tradition has 'shanty'-like work-songs that resemble Welia Wallia in form - e.g., women's working songs from the Scottish Western Isles, and repetitive and improvisable songs from the Irish tradition, like 'Cúnnla'.