fix transmit calculations

[mmsaki]

performance.rst corrections

1. c9bda5a
   1. Transmit 1 byte with 1 mbs: transmit = 1 byte / (1e6 bytes / 1 second) = 0.000001 seconds = 0.001 ms = 1 μs
   2. Transmit 25 Mbs with 10 Mbs: transmit = 25e6 / ( 10e6 / 1 second) = 2.5 seconds
   3. 2.501-second response time and a 2.6-second response time for 1ms and 100ms channel respectively
2. 36cce78
   1. 50 x 10^-3 sec × 45 x 10^6 bytes/sec = 2.25 x 10^6 bytes
   2. 5.5 × 10^6 bits = 688 KB
3. 89568b7
   1. 54 Mbps x 0.33 μs = 18 bytes
   2. 1 Gbps x 230 ms = 230 bytes
   3. 10 Gbps x 40 ms = 400 bytes

[drbruced12]

Most of these changes seem to be the result of not noticing that we use B for bytes (when describing data objects) and b for bits (when describing link speeds).

The suggested change to line 226 misses the fact that a KB is 1024 bytes.

The changes to the table at line 250 would make sense only if link speeds were measured in Bytes per second, but they are in bits per second.

[drbruced12]

Per the review these changes are not correct.