plugin: use namespace prefix osmo_*

Summary of changes:

s/plugin_load_all/osmo_plugin_load_all/g
diff --git a/src/gsm/gprs_cipher_core.c b/src/gsm/gprs_cipher_core.c
index 0ff85e2..7884be0 100644
--- a/src/gsm/gprs_cipher_core.c
+++ b/src/gsm/gprs_cipher_core.c
@@ -53,7 +53,7 @@
 int gprs_cipher_load(const char *path)
 {
 	/* load all plugins available from path */
-	return plugin_load_all(path);
+	return osmo_plugin_load_all(path);
 }
 
 /* function to be called by core code */