For vendors like Juniper, extensibility for sockets is important.  A
good example is socket options that aren't necessarily generic.  To
this end, OSD is added to the socket structure and hooks are defined
for key operations on sockets.  These are:
o   soalloc() and sodealloc()
o   Get and set socket options
o   Socket related kevent filters.

One aspect about hhook that appears to be not fully baked is the return
semantics (the return value from the hook is ignored in hhook_run_hooks()
at the time of commit).  To support return values, the socket_hhook_data
structure contains a 'status' field to hold return values.

Submitted by:	Anuranjan Shukla <anshukla@juniper.net>
Obtained from:	Juniper Networks, Inc.