Update nfsrv_getsocksndseq() for changes in TCP internals since FreeBSD 6.x:
- so_pcb is now guaranteed to be non-NULL and valid if a valid socket
reference is held.
- Need to check INP_TIMEWAIT and INP_DROPPED before assuming inp_ppcb is a
tcpcb, as it might be a tcptw or NULL otherwise.
- tp can never be NULL by the end of the function, so only check
TCPS_ESTABLISHED before extracting tcpcb fields.
The NFS server arguably incorporates too many assumptions about TCP
internals, but fixing that is left for another day.
Reviewed by: bz
Reviewed and tested by: rmacklem
Sponsored by: Juniper Networks
Approved by: re (kib)
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