nlsocket: do not free netlink port on `close()`
nlsocket: do not free netlink port on `close()`

There is no reason to free the port if it can not be reused.

To be investigated.

Bug-Url: https://github.com/svinota/pyroute2/issues/126
little-dude/pyroute2,drzaeus77/pyroute2,nazarewk/pyroute2,drzaeus77/pyroute2,tomislacker/python-iproute2,vodik/pyroute2,mtiny/pyroute2,vodik/pyroute2,simudream/pyroute2,roolebo/pyroute2,roolebo/pyroute2,little-dude/pyroute2,simudream/pyroute2,nazarewk/pyroute2,nazarewk/pyroute2,little-dude/pyroute2,tomislacker/python-iproute2,mtiny/pyroute2