net/mlx5e: Release the label when replacing existing ct entry

In the Linux kernel, the following vulnerability has been resolved:

net/mlx5e: Release the label when replacing existing ct entry

Cited commit doesn't release the label mapping when replacing existing ct
entry which leads to following memleak report:

unreferenced object 0xffff8881854cf280 (size 96):
comm "kworker/u48:74", pid 23093, jiffies 4296664564 (age 175.944s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace:
[<000000002722d368>] __kmalloc+0x4b/0x1c0
[<00000000cc44e18f>] mapping_add+0x6e8/0xc90 [mlx5_core]
[<000000003ad942a7>] mlx5_get_label_mapping+0x66/0xe0 [mlx5_core]
[<00000000266308ac>] mlx5_tc_ct_entry_create_mod_hdr+0x1c4/0xf50 [mlx5_core]
[<000000009a768b4f>] mlx5_tc_ct_entry_add_rule+0x16f/0xaf0 [mlx5_core]
[<00000000a178f3e5>] mlx5_tc_ct_block_flow_offload_add+0x10cb/0x1f90 [mlx5_core]
[<000000007b46c496>] mlx5_tc_ct_block_flow_offload+0x14a/0x630 [mlx5_core]
[<00000000a9a18ac5>] nf_flow_offload_tuple+0x1a3/0x390 [nf_flow_table]
[<00000000d0881951>] flow_offload_work_handler+0x257/0xd30 [nf_flow_table]
[<000000009e4935a4>] process_one_work+0x7c2/0x13e0
[<00000000f5cd36a7>] worker_thread+0x59d/0xec0
[<00000000baed1daf>] kthread+0x28f/0x330
[<0000000063d282a4>] ret_from_fork+0x1f/0x30

Fix the issue by correctly releasing the label mapping.