wifi: mac80211: move interface config to new struct

We'll use bss_conf for per-link configuration later, so
move out all the non-link-specific data out into a new
struct ieee80211_vif_cfg used in the vif.

Some adjustments were done with the following spatch:

    @@
    expression sdata;
    struct ieee80211_vif *vifp;
    identifier var = { assoc, ibss_joined, aid, arp_addr_list, arp_addr_cnt, ssid, ssid_len, s1g, ibss_creator };
    @@
    (
    -sdata->vif.bss_conf.var
    +sdata->vif.cfg.var
    |
    -vifp->bss_conf.var
    +vifp->cfg.var
    )

    @bss_conf@
    struct ieee80211_bss_conf *bss_conf;
    identifier var = { assoc, ibss_joined, aid, arp_addr_list, arp_addr_cnt, ssid, ssid_len, s1g, ibss_creator };
    @@
    -bss_conf->var
    +vif_cfg->var

(though more manual fixups were needed, e.g. replacing
"vif_cfg->" by "vif->cfg." in many files.)

Signed-off-by: Johannes Berg <johannes.berg@intel.com>