Add flags for sniff offload feature

Set flags
```
adb shell setprop persist.device_config.aconfig_flags.bluetooth.com.android.bluetooth.flags.enable_sniff_offload true
adb shell setprop persist.device_config.aconfig_flags.bluetooth.com.android.bluetooth.flags.enable_sniff_offload false
```

Bug: 318614084
Bug: 318786790
Test: atest net_test_bta:BtaDmCustomAlarmTest#sniff_offload_feature__enable_flag
Test: atest net_test_bta:BtaDmCustomAlarmTest#sniff_offload_feature__disable_flag
Flag: EXEMPT, just add flag and prop to disable sniff
Change-Id: Ic398b5833bd06d9fa4fd8c0df6dd4a68d6fbc546