bgpd: Fixed out-of-date comment

When going through the code to write the documentation for local-as,
I discovered that one of the comments was out-of-date.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/bgpd/bgp_attr.c b/bgpd/bgp_attr.c
index f48a543..2cbd7bc 100644
--- a/bgpd/bgp_attr.c
+++ b/bgpd/bgp_attr.c
@@ -1709,7 +1709,7 @@
 }
 
 /* Read attribute of update packet.  This function is called from
-   bgp_update() in bgpd.c.  */
+   bgp_update_receive() in bgp_packet.c.  */
 bgp_attr_parse_ret_t
 bgp_attr_parse (struct peer *peer, struct attr *attr, bgp_size_t size,
 		struct bgp_nlri *mp_update, struct bgp_nlri *mp_withdraw)