dlbAthPeerMcastSnoop is a read-only Counter32 tallying frames passed by multicast snooping for this specific associated wireless client/peer (row keyed by ifIndex and dlbAthPeerIndex) since the interface (or peer entry) came up, and it wraps back to zero once it overflows 32 bits. It is a niche driver-internal counter, so a sysadmin would normally only look at it while diagnosing a specific reported symptom, such as missing multicast traffic or power-save clients not waking correctly, rather than as a routine health metric.