Signal-android: Disable calls for < KK

[righy]

• [x] I have searched open and closed issues for duplicates
• [x] I am submitting a bug report for existing functionality that does not work as intended
• [x] I have read https://github.com/signalapp/Signal-Android/wiki/Submitting-useful-bug-reports
• [x] This isn't a feature request or a discussion topic

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Bug description

When I receive an audio call, Signal restarts right after picking it up. It looks like I can hear the other end for about half a second before it stops. I am then brought to the Signal "enter passphrase" prompt screen.

Steps to reproduce

• Open Signal
• Enter the passphrase to unlock Signal
• Wait until I receive an audio call
• Pick up the call

Actual result: Signal restarts and I am unable to talk with the correspondent.
Expected result: I can talk with the correspondent.

Device info

Device: HTC Desire (codename bravo)
Android version: 4.0.4 (eng.k900.20120624.010557, IMM76I)
Signal version: 4.19.3

Link to debug log

Output of adb logcat (anonymized) just after Signal restarted:
https://gist.github.com/righy/97566347ad1e4c75ed78e9d70b942c8c

[moxie0]

Looks like webrtc's minsdk is greater than your version of Android. We should disable calling for < KitKat to prevent it from crashing.

[haffenloher]

Calls still work fine on Android 4.2 with Signal 4.20.
Is the missing AcousticEchoCanceler class causing the crash? It got added with 4.1 / Jelly Bean: https://developer.android.com/reference/android/media/audiofx/AcousticEchoCanceler

[alan-signal]

We're now >= KK.