wimax/i2400m: increase the maximum number of payloads per message to 60 [v1]

According to Intel Wimax i3200, i5x50 and i6x50 device specification
documents, the maximum number of payloads per message can be up to 60.

Increasing the number of payloads to 60 per message helps to
accommodate smaller payloads in a single transaction. This patch
increases the maximum number of payloads from 12 to 60 per message.

Signed-off-by: Prasanna S. Panchamukhi <prasannax.s.panchamukhi@intel.com>