ui: queue up tunnel mutating on activity scope instead of fragment scope

Fragment scopes get cancelled when the fragment goes away, but we don't
actually want to cancel an in-flight transition in that case. Also,
before when the fragment would cancel, there'd be an exception, and the
exception handler would call Fragment::getString, which in turn called
requireContext, which caused an exception. Work around this by using the
`activity ?: Application.get()` idiom to always have a context for
strings and toasts.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

ui/src/main/java/com/wireguard/android/preference/KernelModuleDisablerPreference.kt

@@ -8,6 +8,7 @@ import android.content.Context
 import android.content.Intent
 import android.util.AttributeSet
 import android.util.Log
+import androidx.lifecycle.lifecycleScope
 import androidx.preference.Preference
 import com.wireguard.android.Application
 import com.wireguard.android.R
@@ -15,6 +16,7 @@ import com.wireguard.android.activity.SettingsActivity
 import com.wireguard.android.backend.Tunnel
 import com.wireguard.android.backend.WgQuickBackend
 import com.wireguard.android.util.UserKnobs
+import com.wireguard.android.util.activity
 import com.wireguard.android.util.lifecycleScope
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.SupervisorJob
@@ -39,7 +41,7 @@ class KernelModuleDisablerPreference(context: Context, attrs: AttributeSet?) : P
     override fun getTitle() = if (state == State.UNKNOWN) "" else context.getString(state.titleResourceId)
 
     override fun onClick() {
-        lifecycleScope.launch {
+        activity.lifecycleScope.launch {
             if (state == State.DISABLED) {
                 setState(State.ENABLING)
                 UserKnobs.setDisableKernelModule(false)