gb/common_vty: use void *

As long the filter doesn't look into the nsvc/bvc structs
there is no need to use the type.
Further it allows to use the same code for NS1 and NS2.

Change-Id: I9b9a70f382a94f1d41142060d5db569f9df865ac
diff --git a/src/gb/common_vty.c b/src/gb/common_vty.c
index a47294b..eb665d5 100644
--- a/src/gb/common_vty.c
+++ b/src/gb/common_vty.c
@@ -40,8 +40,8 @@
 int gprs_log_filter_fn(const struct log_context *ctx,
 			struct log_target *tar)
 {
-	const struct gprs_nsvc *nsvc = ctx->ctx[LOG_CTX_GB_NSVC];
-	const struct gprs_bvc *bvc = ctx->ctx[LOG_CTX_GB_BVC];
+	const void *nsvc = ctx->ctx[LOG_CTX_GB_NSVC];
+	const void *bvc = ctx->ctx[LOG_CTX_GB_BVC];
 
 	/* Filter on the NS Virtual Connection */
 	if ((tar->filter_map & (1 << LOG_FLT_GB_NSVC)) != 0