Use cpumask_var_t instead of struct cpumask to avoid stack overflow with losts of CPUs

Because current kernel has already support thousands of CPUs, so it bring one new APIs for cpumask.
The new one is used to avoid stack overflow.
Use nr_cpu_ids instead of nr_cpumask_bits to check the return value of cpumask_next

It should be check the return value with nr_cpu_ids according to the
comments of both of the cpumask_first and cpumask_next.

Certainly the nr_cpumask_bits has same value as nr_cpu_ids by its definition.
But we should follow the rule of kernel, all of caller in kernel
always use the nr_cpu_ids, not nr_cpumask_bits.
Fix one possible mem leak in fsocket_accept

There is one possible memleak case in fsocket_accept. The out_fd error handler
does not free the newsock by fsock_free_sock.

So I add one new error goto label "out_newfd" to fix it.
Merge branch 'master' of github.com:fastos/fastsocket