cxgb4: add mirror action to TC-MATCHALL offload

Add mirror Virtual Interface (VI) support to receive all ingress
mirror traffic from the underlying device. The mirror VI is
created dynamically, if the TC-MATCHALL rule has a corresponding
mirror action. Also request MSI-X vectors needed for the mirror VI
Rxqs. If no vectors are available, then disable mirror VI support.

v3:
- Replace mirror VI refcount_t with normal u32 variable.

v2:
- Add mutex to protect all mirror VI data, instead of just
  mirror Rxqs.

Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>