Add missing extern "C" declaration.

BUG: 20891299
Change-Id: Iedfd2e8e5bd32014f011352898763bcc0887b6b9
diff --git a/ril/libril/RilSocket.h b/ril/libril/RilSocket.h
index 053df3e..1539c11 100644
--- a/ril/libril/RilSocket.h
+++ b/ril/libril/RilSocket.h
@@ -22,6 +22,8 @@
 
 using namespace std;
 
+extern "C" void *ril_socket_process_requests_loop(void *arg);
+
 /**
  * Abstract socket class representing sockets in rild.
  * <p>