Gosh, could people please read the question - the title of the thread says it all. We are talking
Santiago de Compostela airport, not Madrid, and the poster is asking a very specific question.
I've stayed in San Paio, which is right beside the runway (apartment over the Restaurant Porta de Santiago, or Last 12K, a lovely guest house). San Paoi about a kilometre and a half to the terminal, so a fifteen minute walk would get you there. It is directly on the camino, but not the bus route.
For something directly on the bus route perhaps the
Ruta Jacobea?