net/mlx5e: CT: manage the lifetime of the ct entry object

The ct entry object is accessed by the ct add, del, stats and restore
methods. In addition, it is referenced from several hash tables.

The lifetime of the ct entry object was not managed which triggered race
conditions as in the following kasan dump:
[ 3374.973945] ==================================================================
[ 3374.988552] BUG: KASAN: use-after-free in memcmp+0x4c/0x98
[ 3374.999590] Read of size 1 at addr ffff00036129ea55 by task ksoftirqd/1/15
[ 3375.016415] CPU: 1 PID: 15 Comm: ksoftirqd/1 Tainted: G           O      5.4.31+ #1
[ 3375.055301] Call trace:
[ 3375.060214]  dump_backtrace+0x0/0x238
[ 3375.067580]  show_stack+0x24/0x30
[ 3375.074244]  dump_stack+0xe0/0x118
[ 3375.081085]  print_address_description.isra.9+0x74/0x3d0
[ 3375.091771]  __kasan_report+0x198/0x1e8
[ 3375.099486]  kasan_report+0xc/0x18
[ 3375.106324]  __asan_load1+0x60/0x68
[ 3375.113338]  memcmp+0x4c/0x98
[ 3375.119409]  mlx5e_tc_ct_restore_flow+0x3a4/0x6f8 [mlx5_core]
[ 3375.131073]  mlx5e_rep_tc_update_skb+0x1d4/0x2f0 [mlx5_core]
[ 3375.142553]  mlx5e_handle_rx_cqe_rep+0x198/0x308 [mlx5_core]
[ 3375.154034]  mlx5e_poll_rx_cq+0x2a0/0x1060 [mlx5_core]
[ 3375.164459]  mlx5e_napi_poll+0x1d4/0xa78 [mlx5_core]
[ 3375.174453]  net_rx_action+0x28c/0x7a8
[ 3375.182004]  __do_softirq+0x1b4/0x5d0

Manage the lifetime of the ct entry object by using synchornization
mechanisms for concurrent access.

Fixes: ac991b48 ("net/mlx5e: CT: Offload established flows")
Signed-off-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Oz Shlomo <ozsh@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>