feat(gateway): capture domain name of flow (#10692)

Whenever we route a packet from the Client to a DNS resource, we now
also capture the domain name. If this is the first packet and we are
thus creating a new flow, we'll save that domain in it. Later packets
for the same IP are rolled up under the same flow and thus don't need to
re-set the domain.

Resolves: #10691

scripts/tests/download-concurrent.sh

@@ -35,6 +35,7 @@ rx_bytes=0
 
 for flow in "${flows[@]}"; do
     assert_eq "$(get_flow_field "$flow" "inner_dst_ip")" "172.21.0.101"
+    assert_eq "$(get_flow_field "$flow" "inner_domain")" "download.httpbin"
     rx_bytes+="$(get_flow_field "$flow" "rx_bytes")"
 done
 

scripts/tests/download.sh

@@ -26,4 +26,5 @@ assert_eq "${#flows[@]}" 1
 
 flow="${flows[0]}"
 assert_eq "$(get_flow_field "$flow" "inner_dst_ip")" "172.21.0.101"
+assert_eq "$(get_flow_field "$flow" "inner_domain")" "download.httpbin"
 assert_gteq "$(get_flow_field "$flow" "rx_bytes")" 10000000