src: use namespace prefix osmo_counter*

Summary of changes:

s/struct counter/struct osmo_counter/g
s/counter_inc/osmo_counter_inc/g
s/counter_get/osmo_counter_get/g
s/counter_reset/osmo_counter_reset/g
s/counter_alloc/osmo_counter_alloc/g
s/counter_free/osmo_counter_free
diff --git a/openbsc/src/osmo-bsc_nat/bsc_ussd.c b/openbsc/src/osmo-bsc_nat/bsc_ussd.c
index 69cb7a4..a6fcffc 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_ussd.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_ussd.c
@@ -209,7 +209,7 @@
 	}
 
 	nat = (struct bsc_nat *) bfd->data;
-	counter_inc(nat->stats.ussd.reconn);
+	osmo_counter_inc(nat->stats.ussd.reconn);
 
 	conn = bsc_nat_ussd_alloc(nat);
 	if (!conn) {