[RFC] assign some address families for local use

Hello,

We are working on new protocols and we think that is useful to have some 
address protocol families index assigned for local use. So we will not have 
conflict every time a new protocol is included within the Linux kernel.
Doubt: index 27 and 28 are not assigned to any address family, can be 
explicitly assigned for local use?

We also thought to increase AF_MAX to 64 to avoid to modify it every time.
Doubt: array like af_family_key_strings (net/core/sock.c) will have some NULL 
pointer. I see that a string is specified also for index 27 and 28 even if 
there is not a protocol assigned for these. Is a NULL string a problem for 
these vectors? Typically is used in this way:

    af_family_clock_key_strings[newsk->sk_family]

So, if I set sk_family with an unassigned index I will have a NULL pointer and 
a DEBUG_LOCK_WARN_ON() from lockdep_init_map() (kernel/lockdep.c)


I attached to this email the patch that do these stuff.

-- 
Federico Vaga