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
8 files changed