ipa: Introduce helpers to encode IPA CCM ID RESPONSE

The ipa.c file already contained code to parse an ID RESPONSE into the
'struct ipaccess_unit', but it didn't so far contain code to put
together an ID RESPONSE packet based on that structure.  Let's change
that with ipa_ccm_make_id_resp() and a helper wrapper
ipa_ccm_make_id_resp_from_req().

Change-Id: Icbcd8827a75fd5f3393351c1ca372de85275ad35
diff --git a/include/osmocom/gsm/ipa.h b/include/osmocom/gsm/ipa.h
index 0bb01c5..cabee13 100644
--- a/include/osmocom/gsm/ipa.h
+++ b/include/osmocom/gsm/ipa.h
@@ -37,6 +37,13 @@
 int ipa_ccm_tlv_to_unitdata(struct ipaccess_unit *ud,
 			     const struct tlv_parsed *tp);
 
+
+struct msgb *ipa_ccm_make_id_resp(const struct ipaccess_unit *dev,
+				  const uint8_t *ies_req, unsigned int num_ies_req);
+
+struct msgb *ipa_ccm_make_id_resp_from_req(const struct ipaccess_unit *dev,
+					   const uint8_t *data, unsigned int len);
+
 /* Send an IPA message to the given FD */
 int ipa_send(int fd, const void *msg, size_t msglen);