paging: pass struct osmo_mobile_identity, not encoded IE bytes

In get_paging_mi(), before this, an encoded buffer of Mobile Identity bytes is
returned. Code paths following this repeatedly decode the Mobile Identity
bytes, e.g. for logging. Also, in get_paging_mi(), since the TMSI is read in
from a different encoding than a typical Mobile Identity IE, the TMSI was
manually encoded into a typical Mobile Identity IE. This is essentially a code
dup of osmo_mobile_identity_encode(). Stop this madness.

Instead, in get_paging_mi(), return a decoded struct osmo_mobile_identity. Code
paths after this use the struct osmo_mobile_identity directly without repeated
decoding.

At the point of finally needing an encoded Mobile Identity IE (in
Encoding::write_paging_request()), do a proper osmo_mobile_identity_encode().

Since this may return errors, add an rc check for the caller of
write_paging_request(), gprs_rlcmac_paging_request().

A side effect is stricter validation of the Mobile Identity passing through the
Paging code path. Before, invalid MI might have passed through unnoticed.

Change-Id: Iad845acb0096b75dc453105c9c16b2252879b4ca
diff --git a/src/gprs_rlcmac.cpp b/src/gprs_rlcmac.cpp
index 879ea85..4fb75f7 100644
--- a/src/gprs_rlcmac.cpp
+++ b/src/gprs_rlcmac.cpp
@@ -32,18 +32,20 @@
 
 extern void *tall_pcu_ctx;
 
-int gprs_rlcmac_paging_request(const uint8_t *mi, uint8_t mi_len, uint16_t pgroup)
+int gprs_rlcmac_paging_request(const struct osmo_mobile_identity *mi, uint16_t pgroup)
 {
 	if (log_check_level(DRLCMAC, LOGL_NOTICE)) {
-		struct osmo_mobile_identity omi = {};
 		char str[64];
-		osmo_mobile_identity_decode(&omi, mi, mi_len, true);
-		osmo_mobile_identity_to_str_buf(str, sizeof(str), &omi);
+		osmo_mobile_identity_to_str_buf(str, sizeof(str), mi);
 		LOGP(DRLCMAC, LOGL_NOTICE, "TX: [PCU -> BTS] Paging Request (CCCH) MI=%s\n", str);
 	}
 	bitvec *paging_request = bitvec_alloc(22, tall_pcu_ctx);
 	bitvec_unhex(paging_request, DUMMY_VEC);
-	int plen = Encoding::write_paging_request(paging_request, mi, mi_len);
+	int plen = Encoding::write_paging_request(paging_request, mi);
+	if (plen <= 0) {
+		LOGP(DRLCMAC, LOGL_ERROR, "TX: [PCU -> BTS] Failed to encode Paging Request\n");
+		return -1;
+	}
 	pcu_l1if_tx_pch(paging_request, plen, pgroup);
 	bitvec_free(paging_request);