Change Bouncycastle default AES key size to 128

The default of 192 bit keys was the worst of all choices. 128-bit
runs faster on mobile devices.

(cherry picked from commit ac2a5751dc9578b1f2a8d99906e435993d36c8d6)

Bug: 21085656
Change-Id: Ie4d15ea35e46a157f8c0d43a91e699135e2c58d1
2 files changed