vty: fix style: bssgp node vty prompt

Add trailing space and 'config-' prefix to match our common VTY node prompt
style.

Change-Id: I88db128cad9fcc6e53326b4aed5d06ea9102f328
diff --git a/src/gb/gprs_bssgp_vty.c b/src/gb/gprs_bssgp_vty.c
index 703d130..30ba603 100644
--- a/src/gb/gprs_bssgp_vty.c
+++ b/src/gb/gprs_bssgp_vty.c
@@ -58,7 +58,7 @@
 
 static struct cmd_node bssgp_node = {
 	L_BSSGP_NODE,
-	"%s(bssgp)#",
+	"%s(config-bssgp)# ",
 	1,
 };