build: fix virnetsocket on mingw

Regression introduced in commit 5d30db09.

* src/rpc/virnetsocket.c (virNetSocketNewListenUNIX) [WIN32]: Use
correct signature.

src/rpc/virnetsocket.c

@@ -366,6 +366,7 @@ error:
 #else
 int virNetSocketNewListenUNIX(const char *path ATTRIBUTE_UNUSED,
                               mode_t mask ATTRIBUTE_UNUSED,
+                              uid_t user ATTRIBUTE_UNUSED,
                               gid_t grp ATTRIBUTE_UNUSED,
                               virNetSocketPtr *retsock ATTRIBUTE_UNUSED)
 {