netfilter: nftables: avoid overflows in nft_hash_buckets()

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

netfilter: nftables: avoid overflows in nft_hash_buckets()

Number of buckets being stored in 32bit variables, we have to
ensure that no overflows occur in nft_hash_buckets()

syzbot injected a size == 0x40000000 and reported:

UBSAN: shift-out-of-bounds in ./include/linux/log2.h:57:13
shift exponent 64 is too large for 64-bit type 'long unsigned int'
CPU: 1 PID: 29539 Comm: syz-executor.4 Not tainted 5.12.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:79 [inline]
dump_stack+0x141/0x1d7 lib/dump_stack.c:120
ubsan_epilogue+0xb/0x5a lib/ubsan.c:148
__ubsan_handle_shift_out_of_bounds.cold+0xb1/0x181 lib/ubsan.c:327
__roundup_pow_of_two include/linux/log2.h:57 [inline]
nft_hash_buckets net/netfilter/nft_set_hash.c:411 [inline]
nft_hash_estimate.cold+0x19/0x1e net/netfilter/nft_set_hash.c:652
nft_select_set_ops net/netfilter/nf_tables_api.c:3586 [inline]
nf_tables_newset+0xe62/0x3110 net/netfilter/nf_tables_api.c:4322
nfnetlink_rcv_batch+0xa09/0x24b0 net/netfilter/nfnetlink.c:488
nfnetlink_rcv_skb_batch net/netfilter/nfnetlink.c:612 [inline]
nfnetlink_rcv+0x3af/0x420 net/netfilter/nfnetlink.c:630
netlink_unicast_kernel net/netlink/af_netlink.c:1312 [inline]
netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1338
netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1927
sock_sendmsg_nosec net/socket.c:654 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:674
____sys_sendmsg+0x6e8/0x810 net/socket.c:2350
___sys_sendmsg+0xf3/0x170 net/socket.c:2404
__sys_sendmsg+0xe5/0x1b0 net/socket.c:2433
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46