Scheduler: new REUSEPORT balancing method/architecture.

Starting from Linux Kernel 3.9, there is a new TCP/UDP socket option which allows
to bind same port and address from multiples threads (or any instance under the
same process context).

This patch implements the SO_REUSEPORT TCP Flag if the running Kernel is >= 3.9,
so on that mode each working thread create it own socket that bind the same address,
with this implementation we reduce the number of system calls involved when a new
connection arrives, avoid lookup the lowest loaded thread and also we allow the
Kernel to perform a better Scheduling on SMP systems that requires to scale.

If the detected Kernel is lower than 3.9, it will use the old Fair Balancing
mechanism.

Signed-off-by: Eduardo Silva <edsiper@gmail.com>
Scheduler: Little improvements over REUSEPORT implementation.

Signed-off-by: Eduardo Silva <edsiper@gmail.com>
Kernel: new features interfaces and core flags

Signed-off-by: Eduardo Silva <edsiper@gmail.com>