struct kinfo_file changes needed for lsof to work using only usermode APIs`

Add kf_pipe_buffer_[in/out/size] fields to kf_pipe, and populate them.

Add a kf_kqueue struct to the kf_un union, to allow querying kqueue state,
and populate it.

Populate the kf_sock_rcv_sb_state and kf_sock_snd_sb_state fields in
kf_sock for INET/INET6 sockets, and populate all other fields for all
transport layer protocols, not just TCP.

Bump __FreeBSD_version.

Differential revision: https://reviews.freebsd.org/D34184
Reviewed by: jhb, kib, se
MFC after: 1 week