Use cythonized SO_REUSEPORT rather than the unwrapped native one. (#609)

Fixes #550

Co-authored-by: Fantix King <fantix.king@gmail.com>

Author: ptribble

uvloop/includes/uv.pxd

@@ -57,7 +57,7 @@ cdef extern from "uv.h" nogil:
     cdef int SOL_SOCKET
     cdef int SO_ERROR
     cdef int SO_REUSEADDR
-    cdef int SO_REUSEPORT
+    # use has_SO_REUSEPORT and SO_REUSEPORT in stdlib.pxi instead
     cdef int AF_INET
     cdef int AF_INET6
     cdef int AF_UNIX

uvloop/loop.pyx

@@ -1775,7 +1775,7 @@ cdef class Loop:
                         if reuse_address:
                             sock.setsockopt(uv.SOL_SOCKET, uv.SO_REUSEADDR, 1)
                         if reuse_port:
-                            sock.setsockopt(uv.SOL_SOCKET, uv.SO_REUSEPORT, 1)
+                            sock.setsockopt(uv.SOL_SOCKET, SO_REUSEPORT, 1)
                         # Disable IPv4/IPv6 dual stack support (enabled by
                         # default on Linux) which makes a single socket
                         # listen on both address families.