netfilter: nf_tables: all transaction allocations can now sleep

netfilter: nf_tables: all transaction allocations can now sleep

Now that nft_setelem_flush is not called with rcu read lock held or
disabled softinterrupts anymore this can now use GFP_KERNEL too.

This is the last atomic allocation of transaction elements, so remove
all gfp_t arguments and the wrapper function.

This makes attempts to delete large sets much more reliable, before
this was prone to transient memory allocation failures.

Signed-off-by: Florian Westphal <fw@strlen.de>