o Provide a compatibility shim for netstat(1) to obtain output queue

o Provide a compatibility shim for netstat(1) to obtain output queue
  drops via NET_RT_IFLISTL sysctl. The sysctl handler appends oqdrops
  at the end of struct if_msghdrl, and netstat(1) sees that as an
  additional field of struct if_data. This allows us to fetch the data
  keeping ABI and API compatibility.
  This is direct commit to stable/10.

o Merge r263331 from head, to restore printing of queue drops.

Sponsored by:	Nginx, Inc.
Sponsored by:	Netflix

git-svn-id: svn://svn.freebsd.org/base/stable/10@264076 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f