qcacld-3.0: Add time slice duty cycle in wifi_interface_info

Android S VTS test case GetLinkLayerStats_1_5 need get interface time
slice duty cycle info. VTS will get it over vendor command
QCA_NL80211_VENDOR_SUBCMD_LL_STATS_GET.

So, we need put time slice duty cycle percentage in structure
wifi_interface_info.

Change-Id: Iff644b4b1ed6dd34badc2008d2957c98e0207aa6
CRs-Fixed: 3040005