Fix missing extern.

Change-Id: Iaf7c85b49350e0716d40edb36129714ca47fdb11
diff --git a/rild/rild.c b/rild/rild.c
index 5757a39..8d3fb6a 100644
--- a/rild/rild.c
+++ b/rild/rild.c
@@ -52,6 +52,7 @@
 extern void RIL_onRequestComplete(RIL_Token t, RIL_Errno e,
                            void *response, size_t responselen);
 
+extern void RIL_setRilSocketName(char *);
 
 #if defined(ANDROID_MULTI_SIM)
 extern void RIL_onUnsolicitedResponse(int unsolResponse, const void *data,