stats: Add osmo_ name prefix to identifiers

Since the the stat_item and stats functions and data types are meant
to be exported, they get an osmo_ prefix.

Sponsored-by: On-Waves ehf

[hfreyther: Prepended the enum values too. This was requested by
Jacob]
diff --git a/include/osmocom/vty/misc.h b/include/osmocom/vty/misc.h
index 99c2ee6..f3b46db 100644
--- a/include/osmocom/vty/misc.h
+++ b/include/osmocom/vty/misc.h
@@ -14,7 +14,7 @@
 			    struct rate_ctr_group *ctrg);
 
 void vty_out_stat_item_group(struct vty *vty, const char *prefix,
-			     struct stat_item_group *statg);
+			     struct osmo_stat_item_group *statg);
 
 void vty_out_statistics_full(struct vty *vty, const char *prefix);