qlcnic: refactor Tx/SDS ring calculation and validation in driver.

o Current driver has duplicate code for validating user input
  for changing Tx/SDS rings using set_channel ethtool interface.
  This patch removes duplicate code and refactored Tx/SDS ring
  validation for 82xx/83xx/84xx series adapter.
o Refactored code now calculates maximum Tx/Rx ring driver can
  support based on Default, NPAR and SRIOV PF/VF mode of driver.

Signed-off-by: Himanshu Madhani <himanshu.madhani@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>