lapdm: Append RSL_IE_OSMO_ABS_FRAME_NUMBER to RSLms msgs towards upper layers

This makes it possible to track GSM time in the upper layers.
The existing RSL_IE_FRAME_NUMBER and RSL_IE_STARTNG_TIME cannot be used
there, since those are 16bit fields containing Relative FN values.

The IE needs to be added before the L3_INFO one, because user code
usually assumes the msgb->l3 pointing to L3_INFO value extends until the
end of the message, using msgb3_len(msg). Regarding having an extra IE
at the middle, it's not a big problem since the libosmocore version
submitting this commit to the upper layers is the same which will also
be parsing it through rsl_tlv_parse() later on by the app.

Related: OS#3626
Change-Id: Id62c18f49f270449067b25b7104eb8b47f1955ec
diff --git a/tests/lapd/lapd_test.c b/tests/lapd/lapd_test.c
index 2f2a7f4..bae73c2 100644
--- a/tests/lapd/lapd_test.c
+++ b/tests/lapd/lapd_test.c
@@ -359,7 +359,7 @@
 		struct abis_rsl_rll_hdr hdr;
 
 		printf("MS: Verifying incoming primitive.\n");
-		OSMO_ASSERT(msg->len == sizeof(struct abis_rsl_rll_hdr));
+		OSMO_ASSERT(msg->len >= sizeof(struct abis_rsl_rll_hdr));
 
 		/* verify the header */
 		memset(&hdr, 0, sizeof(hdr));