ice: Add code for DCB initialization part 3/4

This patch adds a new function ice_pf_dcb_cfg (and related helpers)
which applies the DCB configuration obtained from the firmware. As
part of this, VSIs/netdevs are updated with traffic class information.

This patch requires a bit of a refactor of existing code.

1. For a MIB change event, the associated VSI is closed and brought up
   again. The gap between closing and opening the VSI can cause a race
   condition. Fix this by grabbing the rtnl_lock prior to closing the
   VSI and then only free it after re-opening the VSI during a MIB
   change event.

2. ice_sched_query_elem is used in ice_sched.c and with this patch, in
   ice_dcb.c as well. However, ice_dcb.c is not built when CONFIG_DCB is
   unset. This results in namespace warnings (ice_sched.o: Externally
   defined symbols with no external references) when CONFIG_DCB is unset.
   To avoid this move ice_sched_query_elem from ice_sched.c to
   ice_common.c.

Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>