add a VTY command which shows a specific HNB

Add the 'show hnb NAME' VTY command which displays just
one specific HNB, addressed by its identity string.
This augments the functionality provided by 'show hnb all'.

Change-Id: Iab12aa4ab090b72c472358b84daf6919b30747f6
Related: OS#2774
diff --git a/include/osmocom/iuh/hnbgw.h b/include/osmocom/iuh/hnbgw.h
index db49dc1..4848c2f 100644
--- a/include/osmocom/iuh/hnbgw.h
+++ b/include/osmocom/iuh/hnbgw.h
@@ -151,6 +151,7 @@
 extern void *talloc_asn1_ctx;
 
 struct hnb_context *hnb_context_by_id(struct hnb_gw *gw, uint32_t cid);
+struct hnb_context *hnb_context_by_identity_info(struct hnb_gw *gw, const char *identity_info);
 unsigned hnb_contexts(const struct hnb_gw *gw);
 
 struct ue_context *ue_context_by_id(struct hnb_gw *gw, uint32_t id);