Sa525m has 4 CPU cores, enable NAPI to make better use of CPUs.
It also avoid following kernel warning during driver unload:
"
 Call trace:
  __free_irq+0x1d8/0x374
  free_irq+0x34/0x74
  pld_srng_free_irq+0x44/0xd8 [qca6490]
  hif_pci_deconfigure_grp_irq+0x78/0xf8 [qca6490]
  ...
  ret_from_fork+0x10/0x20
"

Change-Id: Ifa75c522d2df42ae9e57c47cb6240522588898fa
CRs-Fixed: 3838454