[$] Better visibility into packet-dropping decisions

Dropped packets are a fact of life in networking; there can be any numberof reasons why a packet may not survive the journey to its destination.Indeed, there are so many ways that a packet can meet its demise that itcan be hard for an administrator to tell why packets are being dropped.That, in turn, can make life difficult in times when users are complainingabout high packet-loss rates. Starting with 5.17, the kernel is gettingsome improved instrumentation that should shed some light on why the kerneldecides to route packets into the bit bucket.