iproute2: Add ll_index_to_addr function

After calling ll_init_map, all of the information stored in the link-layer map
can be retrieved by function calls (ll_index_to_*), except for the link-layer
address. This patch fills the gap by adding a ll_index_to_addr function.
Changes welcome.
Signed-off-by: David Ward <david.ward@ll.mit.edu>

include/ll_map.h

@@ -9,5 +9,7 @@ extern const char *ll_index_to_name(unsigned idx);
 extern const char *ll_idx_n2a(unsigned idx, char *buf);
 extern int ll_index_to_type(unsigned idx);
 extern unsigned ll_index_to_flags(unsigned idx);
+extern unsigned ll_index_to_addr(unsigned idx, unsigned char *addr,
+				 unsigned alen);
 
 #endif /* __LL_MAP_H__ */

lib/ll_map.c

@@ -134,6 +134,27 @@ unsigned ll_index_to_flags(unsigned idx)
 	return 0;
 }
 
+unsigned ll_index_to_addr(unsigned idx, unsigned char *addr,
+			  unsigned alen)
+{
+	struct idxmap *im;
+
+	if (idx == 0)
+		return 0;
+
+	for (im = idxmap[idx&0xF]; im; im = im->next) {
+		if (im->index == idx) {
+			if (alen > sizeof(im->addr))
+				alen = sizeof(im->addr);
+			if (alen > im->alen)
+				alen = im->alen;
+			memcpy(addr, im->addr, alen);
+			return alen;
+		}
+	}
+	return 0;
+}
+
 unsigned ll_name_to_index(const char *name)
 {
 	static char ncache[16];