Kernel provides us with enough information to display all possible
connections between UNIX sockets.
o Store unp_conn, xu_firstref and xu_nextref in the faddr of a UNIX sock.
o Build tree of file descriptors, indexed by the socket pointer.
o In displaysock() print out all possible information:
1) if socket is bound, print name of this socket
2) if socket has connected to a peer with a name, print peers name
3) if socket has connected to a peer without a name, print [pid fd]
4) if a bound socket has received connections, print list of them
as [pid fd]
Previously, only 1) either 2) were printed.
Reviewed by: tuexen
Differential revision: https://reviews.freebsd.org/D35726
2c436d4890