qcacmn: Add vdev-mlme caps MASK for restrict_offchannel

Adds new vdev-mlme caps mask WLAN_VDEV_C_RESTRICT_OFFCHAN for
tracking restrict offchannel setting.
When this bit is set any operations which can cause the AP/GO
to leave the operating channel are avoided.

Also reads vdev-mlme caps:WLAN_VDEV_C_RESTRICT_OFFCHAN in function
policy_mgr_is_dnsc_set() to determine if Do_Not_Switch_Channel
is enabled.
Moves declaration of policy_mgr_is_dnsc_set() to
wlan_policy_mgr_api.h so that it can be used outside of policy manager.

Change-Id: I53013af5f4c72917f862630e63333951ec75ce8c
CRs-Fixed: 2050999
4 files changed