I attached a patch proposal, it adds mlockall_pid() and munlockall_pid()
syscalls (I've included only the mm/mlock.c file).

I generalized the present code to work on a pointer `p` that in case of
mlockall() and munlockall() corresponds to `current`.
Instead, with mlockall_pid() and munlockall_pid(), after permission checks,
it gets the task_struct from find_task_by_vpid.

I tested the syscalls and they seem ok, but I'm not sure how to test them
thoroughly.


Cheers,
Federico