When mirror VI is enabled, replicate various VI config params
enabled on main VI to mirror VI. These include replicating MTU,
promiscuous mode, all-multicast mode, and enabled netdev Rx
feature offloads.

v3:
- Replace mirror VI refcount_t with normal u32 variable.
- Add back calling cxgb4_port_mirror_start() in cxgb_open(), which
  was there in v1, but got missed in v2 during refactoring.

v2:
- Simplify the replication code by refactoring t4_set_rxmode()
  to handle mirror VI, instead of duplicating the t4_set_rxmode()
  calls in multiple places.
Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>