staging: brcm80211: remove _brcmf_sysioc_thread in fullmac

_brcmf_sysioc_thread is handling deferred jobs from 4 callers. Use
work queue to handle set_mac_address/set_multicast_list requests.
brcmf_add_if/brcmf_del_if never run in atomic context and can call
brcmf_op_if directly.

Reported-by: Johannes Berg <johannes@sipsolutions.net>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Franky Lin <frankyl@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>