Marcel, Israel and Syria are still technically in a state of war. There's no peace treaty between the two states. Violating airspace of one country by another in a time of war isn't called international law violation. Syria's facilitation of weapons delivery to Hizbullah isn't an act of peace either.
U.S. confirms ISIS computer expert killed in air strike (Reuters)
from the article: Assad revokes citizenship of politician who visited Knesset