mpdu: Validate action frame minimum length

Action frames must at least have the Category byte

src/mpdu.c

@@ -587,7 +587,7 @@ static bool validate_mgmt_mpdu(const struct mmpdu_header *mpdu, int len,
 		return validate_deauthentication_mmpdu(mpdu, len, offset);
 	case MPDU_MANAGEMENT_SUBTYPE_ACTION:
 	case MPDU_MANAGEMENT_SUBTYPE_ACTION_NO_ACK:
-		return true;
+		return *offset + 1 <= len;
 	default:
 		return false;
 	}