Add options setting number of tile groups or MTU.
Default MTU size is 0, which implies a fixed number of tile groups. MTU matching overrides fixed tile group. MTU matching will succeed unless a single tile is bigger than the MTU. --mtu-size is in bytes, and includes headers but not transport/wrapper overheads Change-Id: I2b70bd41b175b54273b02d836f2a84011f617a7c