CVE-2021-47312

In the Linux kernel, the following vulnerability has been resolved:
netfilter: nf_tables: Fix dereference of null pointer flow In the case
where chain->flags & NFT_CHAIN_HW_OFFLOAD is false then
nft_flow_rule_create is not called and flow is NULL. The subsequent error
handling execution via label err_destroy_flow_rule will lead to a null
pointer dereference on flow when calling nft_flow_rule_destroy. Since the
error path to err_destroy_flow_rule has to cater for null and non-null
flows, only call nft_flow_rule_destroy if flow is non-null to fix this
issue. Addresses-Coverity: (“Explicity null dereference”)