Make sure to set the latency send date when starting the monitor. (#630)

Required:

Task/Issue URL: https://app.asana.com/0/0/1206412872188595/f
iOS PR: duckduckgo/iOS#2368
macOS PR: duckduckgo/macos-browser#2103
What kind of version bump will this require?: Patch

Description:

This PR fixes a bug in the latency monitor. See parent task for more info.

Sources/NetworkProtection/Diagnostics/NetworkProtectionLatencyMonitor.swift

@@ -92,6 +92,8 @@ public actor NetworkProtectionLatencyMonitor {
     public func start(serverIP: IPv4Address, callback: @escaping (Result) -> Void) {
         os_log("⚫️ Starting latency monitor", log: .networkProtectionLatencyMonitorLog)
 
+        lastLatencyReported = Date()
+
         latencyCancellable = latencySubject.eraseToAnyPublisher()
             .receive(on: DispatchQueue.main)
             .scan(ExponentialGeometricAverage()) { measurements, latency in