slirp: Port redirection option behave differently on Linux and Windows

slirp: Port redirection option behave differently on Linux and Windows

port redirection code uses SO_REUSEADDR socket option before binding to
host port. Behavior of SO_REUSEADDR is different on Windows and Linux.
Relaunching QEMU with same host and guest port redirection values on Linux
throws error but on Windows it does not throw any error.
Problem is discussed in http://lists.gnu.org/archive/html/qemu-devel/2013-04/msg03089.html

Signed-off-by: Taimoor Mirza <tmirza@codesourcery.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>