Change help text for client_throttle_max_bps in OpenSimDefaults.ini to state it is in bytes, not bits

This is the same as already done for scene_throttle_max_bps
Internally, the token buckets are in bytes and the other help text makes it clear that the number is bytes per second
(though with the wrong assumption that 1 mbit = 1024 * 1024 bits whereas 1 mbit = 1000 kbits = 1000000 bits)