libbsc, osmo-bsc{, _nat}: Prevent unaligned access when casting TLVP_VAL

foo = *((uintXX_t *) TLVP_VAL(...) can lead to unaligned access. To
prevent that use tlvp_valXX_unal() to get the values.
diff --git a/openbsc/src/osmo-bsc_nat/bsc_mgcp_utils.c b/openbsc/src/osmo-bsc_nat/bsc_mgcp_utils.c
index 22b8a35..e13827b 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_mgcp_utils.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_mgcp_utils.c
@@ -191,7 +191,7 @@
 		return -1;
 	}
 
-	cic = ntohs(*(uint16_t *)TLVP_VAL(&tp, GSM0808_IE_CIRCUIT_IDENTITY_CODE));
+	cic = ntohs(tlvp_val16_unal(&tp, GSM0808_IE_CIRCUIT_IDENTITY_CODE));
 	timeslot = cic & 0x1f;
 	multiplex = (cic & ~0x1f) >> 5;