MINOR: proxy_protocol: Ingest PP2_TYPE_UNIQUE_ID on incoming connections

This patch reads a proxy protocol v2 provided unique ID and makes it
available using the `fc_pp_unique_id` fetch.
diff --git a/include/proto/connection.h b/include/proto/connection.h
index fb264d2..9b8eb8a 100644
--- a/include/proto/connection.h
+++ b/include/proto/connection.h
@@ -325,6 +325,7 @@
 	conn->src = NULL;
 	conn->dst = NULL;
 	conn->proxy_authority = NULL;
+	conn->proxy_unique_id = IST_NULL;
 }
 
 /* sets <owner> as the connection's owner */
@@ -458,6 +459,10 @@
 		pool_free(pool_head_authority, conn->proxy_authority);
 		conn->proxy_authority = NULL;
 	}
+	if (isttest(conn->proxy_unique_id)) {
+		pool_free(pool_head_uniqueid, conn->proxy_unique_id.ptr);
+		conn->proxy_unique_id = IST_NULL;
+	}
 
 	/* By convention we always place a NULL where the ctx points to if the
 	 * mux is null. It may have been used to store the connection as a
diff --git a/include/types/connection.h b/include/types/connection.h
index 0c2d960..30cb895 100644
--- a/include/types/connection.h
+++ b/include/types/connection.h
@@ -469,6 +469,7 @@
 	char *proxy_authority;	      /* Value of authority TLV received via PROXYv2 */
 	unsigned int idle_time;                 /* Time the connection was added to the idle list, or 0 if not in the idle list */
 	uint8_t proxy_authority_len;  /* Length of authority TLV received via PROXYv2 */
+	struct ist proxy_unique_id;  /* Value of the unique ID TLV received via PROXYv2 */
 };
 
 /* PROTO token registration */