illumos gate

This ticket covers issues with the following manual pages:

• net_hook_register
• net_protocol_lookup
• net_protcol_release
• net_instance_alloc
• hook_t
• net_instance_t

All of these manual pages doesn't match the reality of the function. Specifically it may have the incorrect number of arguments and wrong types.

net_instance_alloc specifies the wrong variable to use for a version.

The hook_t doesn't mention the important semantics of the return value of the h_func. Okay, really there is no documentation for it, except kind of gleamed from an example on opensolaris.org and the source code.

net_instance_t needs to mention that it is illegal for nin_create to return NULL.