port allocator: make used port bitmap global

port allocator: make used port bitmap global

Host tcp4/tcp6 ports is a global resource thus we need to make
port accounting also global or we have issues described in [1] when
port allocator ranges of different instances are overlapped (which
is by default for qemu for example).

Let's have only one global port allocator object that take care
of the entire ports range (0 - 65535) and introduce port range object
for clients to specify desired auto allocation band.

[1] https://www.redhat.com/archives/libvir-list/2017-December/msg00600.html

Signed-off-by: Nikolay Shirokovskiy <nshirokovskiy@virtuozzo.com>