USB: u_ether: Increase the IN endpoint buffer allocation

Some UDC may require allocation of some extra bytes for
TX buffer due to hardware requirement. Add necessary
changes for the same.

Change-Id: I2d0e636e0a876cce16077fa9929d92f13e383dd2
Signed-off-by: Tarun Gupta <tarung@codeaurora.org>
Signed-off-by: Sivasri Kumar Vanka <sivasri@codeaurora.org>