linux-user: add RTA_PRIORITY in netlink

Used by fedora21 on ppc64 in the network initialization

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index beeb23d..31143b3 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -2600,6 +2600,7 @@
     case RTA_GATEWAY:
         break;
     /* u32 */
+    case RTA_PRIORITY:
     case RTA_OIF:
         u32 = RTA_DATA(rtattr);
         *u32 = tswap32(*u32);