iwlwifi: set interrupt coalescing timer range and default

For interrupt coalescing timer, the CSR_INT_COALESCING is an 8 bit
register in 32-usec unit, the range can go from 0x00 - 0xFF. set the
range and default timeout value for both calibration mode and operation mode.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>