Bugfix/issue 1867 Bluetooth notification error fix

[JulianKast]

Fixes #1867

This PR is [ready] for review.

Risk

This PR makes [no] API changes.

Testing Plan

• I have verified that I have not introduced new warnings in this PR (or explain why below)
• I have run the unit tests with this PR
• I have tested this PR against Core and verified behavior (if applicable, if not applicable, explain why below).
• I have tested Android

Unit Tests

n/a

Core Tests

Test 1

1. Install SDL app to phone
2. Connect to tdk via Bluetooth
3. Observe SDL app connection
4. Disconnect from tdk by clicking on the BT connection and clicking disconnect on the phone.
   Repeat steps 2-4 up to 30 times
   Observe:
   Bluetooth notification does not appear for too many apps using Bluetooth.

Test 2

1. Install SDL app to phone
2. Connect to TDK
3. Disconnect Bluetooth from TDK, but leave Bluetooth turned on.
4. Install and run this app https://github.com/shiniwat/consumespp and let it consume all available SPP resources
5. Connect to TDK
   Observe:
   Bluetooth notification appears for too many apps using Bluetooth

Core version / branch / commit hash / module tested against: Sync 3
HMI name / version / branch / commit hash / module tested against: Sync 3

Summary

Add a check to see if RouterService is in the Foreground before sending the spp notification.

Changelog

Bug Fixes

• Fixes an issue where the spp notification was being sent to the users in error.

CLA

• I have signed the CLA

[joeygrover]

Small change requested for thread safety but otherwise solution works well.

[joeygrover]

This variable should actually be accessed with this lock. It will ensure that the correct state is returned here.

Suggested change

	// Check first to see if the RouterService is in the Foreground
	// This is to prevent the notification appearing in error
	if (!this.isForeground) {
	return;
	}
	synchronized (FOREGROUND_NOTIFICATION_LOCK) {
	// Check first to see if the RouterService is in the Foreground
	// This is to prevent the notification appearing in error
	if (!this.isForeground) {
	return;
	}
	}