http: warn once for response 100-continue already seen

Avoids pushing multiple log messages, when the consumer will
only set one app-layer event for the tx
Also, this is a warning, not an error, as we continue parsing.

Ticket: 8867
(cherry picked from commit 4dd7ebf079)

rust/htp/src/response.rs

@@ -446,10 +446,14 @@ impl ConnectionParser {
                 _ => {
                     let response_tx = self.response_mut().unwrap();
                     if response_tx.seen_100continue {
-                        htp_error!(
+                        let mut flags = 0; // unused but needed by macro
+                        htp_warn_once!(
                             self.logger,
                             HtpLogCode::CONTINUE_ALREADY_SEEN,
-                            "Already seen 100-Continue."
+                            "Already seen 100-Continue.",
+                            self.response_mut().unwrap().flags,
+                            flags,
+                            HtpFlags::FIELD_100_CONTINUE
                         );
                     }
                     // Expecting to see another response line next.

rust/htp/src/util.rs

@@ -143,6 +143,8 @@ impl HtpFlags {
     pub const RESPONSE_MISSING_BYTES: u64 = (0x0020_0000_0000 | Self::MISSING_BYTES);
     /// Too many headers, log only once.
     pub const HEADERS_TOO_MANY: u64 = 0x0040_0000_0000;
+    /// 100-Continue already seen.
+    pub const FIELD_100_CONTINUE: u64 = 0x0080_0000_0000;
 }
 
 #[allow(clippy::upper_case_acronyms)]