Start to use struct osmo_auth_vector from gsm_auth_tuple

Rather than having a 'private' structure for kc, sres and rand, we
now finally (with 4 years delay) use osmo_auth_vector from libosmogsm,
which encapsulates authentication vectors that can be either GSM
triplets or UMTS quintuples or a combination of both.

gsm_auth_tuple becomes a wrapper around osmo_auth_vector, adding
use_count and key_seq to it.

key_seq is no longer initialized inside gprs_gsup_messages.c, as there
is no CKSN / key_seq inside the message anyway.  If a usre of the code
needs key_seq, they need to manage it themselves.
diff --git a/openbsc/src/libmsc/vty_interface_layer3.c b/openbsc/src/libmsc/vty_interface_layer3.c
index 790fedf..4c2088a 100644
--- a/openbsc/src/libmsc/vty_interface_layer3.c
+++ b/openbsc/src/libmsc/vty_interface_layer3.c
@@ -94,13 +94,13 @@
 		vty_out(vty, "     seq # : %d%s",
 			atuple.key_seq, VTY_NEWLINE);
 		vty_out(vty, "     RAND  : %s%s",
-			osmo_hexdump(atuple.rand, sizeof(atuple.rand)),
+			osmo_hexdump(atuple.vec.rand, sizeof(atuple.vec.rand)),
 			VTY_NEWLINE);
 		vty_out(vty, "     SRES  : %s%s",
-			osmo_hexdump(atuple.sres, sizeof(atuple.sres)),
+			osmo_hexdump(atuple.vec.sres, sizeof(atuple.vec.sres)),
 			VTY_NEWLINE);
 		vty_out(vty, "     Kc    : %s%s",
-			osmo_hexdump(atuple.kc, sizeof(atuple.kc)),
+			osmo_hexdump(atuple.vec.kc, sizeof(atuple.vec.kc)),
 			VTY_NEWLINE);
 	}