bindresvport() uses two static variables port and startport which are not

bindresvport() uses two static variables port and startport which are not
protected. It is not safe when in multithread circumstance.

bindresvport() select a port number from the range 512 to 1023, when in
multithread circumstance, the port may be 1024. So the static variables will be
protected.

Signed-off-by: Peng Haitao <penght@cn.fujitsu.com>
Reviewed-by: Carlos O'Donell <carlos@systemhalted.org>