ath6kl: Avoid taking struct as argument in ath6kl_wmi_set_ip_cmd

In this way, caller is free to pass only the value of IP addr
to configure.

In addition to this,
  * 'ips' variable data type in struct wmi_set_ip_cmd is changed
     from __le32 to __be32 in order to match network byte order.
  *  ipv4_is_multicast() is used to validate multicast ip addr.
  *  New argument if_idx is added to supply correct vif index
     to ath6kl_wmi_cmd_send().

This will be used in the next patch.

Signed-off-by: Raja Mani <rmani@qca.qualcomm.com>
Signed-off-by: Thirumalai Pachamuthu <tpachamu@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>