tx5 ignores response value field and misreads MAX_BW opcode

tx5 never reads the 8-bit value field of a response, so a THROTTLE with a competitor count and a MAX_BW cap are treated identically by opcode alone. MAX_BW (4'b1111) in tx5 clears the stop latch and zeroes severity, which is the opposite meaning from the scheduler's bandwidth-cap response. Any MAX_BW path through tx5 will behave incorrectly until this is reconciled.