BUG/MEDIUM: quic: Missing AEAD TAG check after removing header protection

After removing the packet header protection, we can check the packet is long
enough to contain a 16 bytes length AEAD TAG (at this end of the packet).
This test was missing.

Must be backported to 2.6.
diff --git a/src/xprt_quic.c b/src/xprt_quic.c
index 3705608..1589834 100644
--- a/src/xprt_quic.c
+++ b/src/xprt_quic.c
@@ -4628,6 +4628,11 @@
 
 		/* The AAD includes the packet number field found at <pn>. */
 		pkt->aad_len = pn - beg + pkt->pnl;
+		if (pkt->len - pkt->aad_len < QUIC_TLS_TAG_LEN) {
+			TRACE_PROTO("Too short packet", QUIC_EV_CONN_TRMHP, qc);
+			goto err;
+		}
+
 		qpkt_trace = pkt;
 	}
 	else {