On a very literal level, Simon is requesting that Ralph suck his wound. A person would supposedly do this if the wound is poisoned, which Ralph's would is not. He was gored by a pig/boar; he was not poisoned by a snake or anything like that. Sucking on the wound won't do anything. In fact, even if it were a snake bite, sucking the wound wouldn't do anything. That's urban myth.
It's possible that Simon is confusing Berengaria with Eleanor of Castile. She was English royalty that supposedly saved her husband's life by sucking the poison out of the wound. Berengaria, on the other hand, has nothing to do with poison. She was the wife of Richard I of England. She was also rumored to be homosexual, which means she married for political reasons vs. romantic reasons.
Why Golding put the mistaken reference in is unknown. I think the significance of the mistake is to make readers research both women and make comparisons to characters in the novel. Eleanor of Castile is like Ralph because both characters are willing to do whatever it takes to save another human. Berengaria is like Jack, because he will do whatever it takes to get more power.
There are likely two things that Simon might be referring to, but it is difficult to figure out exactly what was mean without being able to ask William Golding himself.
One possibility is a reference to a ship that was sunk in WWI, but it is nearly impossible to find anything really connecting this to that.
The second, and more likely, is that Simon confused Berengaria of Navarre with Eleanor of Castile. They were both noble women of some fame in English folklore but it was Eleanor that was supposed to have sucked the poison out of a wound that saved her husband's life.