qcacld-3.0: Add support to config num of chains over vendor cmd

Currently there is only SETANTENNAMODE ioctl command to configure
number of chains to firmware.

Add support to configure the number of chains over the nl vendor
command QCA_WLAN_VENDOR_ATTR_CONFIG_NUM_TX_CHAINS and
QCA_WLAN_VENDOR_ATTR_CONFIG_NUM_RX_CHAINS.

This new interface will configure the number of chains per vdev
dynamically.

Change-Id: Iff22d886529f6d8fb205d668eba8928039620a20
CRs-Fixed: 2756647