net: Kirkwood_egiga.c bugfixes for rx path

Cosmetic changes: Few comments updated
Functionality: Rx packet frame size is programming should
be done when port is in disabled state. this is corrected

Signed-off-by: Prafulla Wadaskar <prafulla@marvell.com>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>