It means he was impressively turned out in something like this, a covering for the lower leg that buttoned up the side. They're "largely obsolete" now and probably were beginning to become so when this book was written---yet another example of how Bertram's Hotel is a "throwback" to earlier times. They date from a time when bishops did their work on horseback.
Tourist in Gaiters - TIME (note date of article!)
- For Teachers