netfilter: nfnetlink: place subsys mutexes in distinct lockdep classes

From time to time there are lockdep reports similar to this one:

 WARNING: possible circular locking dependency detected
 ------------------------------------------------------
 000000004f61aa56 (&table[i].mutex){+.+.}, at: nfnl_lock [nfnetlink]
 but task is already holding lock:
 [..] (&net->nft.commit_mutex){+.+.}, at: nf_tables_valid_genid [nf_tables]
 which lock already depends on the new lock.
 the existing dependency chain (in reverse order) is:
 -> #1 (&net->nft.commit_mutex){+.+.}:
 [..]
        nf_tables_valid_genid+0x18/0x60 [nf_tables]
        nfnetlink_rcv_batch+0x24c/0x620 [nfnetlink]
        nfnetlink_rcv+0x110/0x140 [nfnetlink]
        netlink_unicast+0x12c/0x1e0
 [..]
        sys_sendmsg+0x18/0x40
        linux_sparc_syscall+0x34/0x44
 -> #0 (&table[i].mutex){+.+.}:
 [..]
        nfnl_lock+0x24/0x40 [nfnetlink]
        ip_set_nfnl_get_byindex+0x19c/0x280 [ip_set]
        set_match_v1_checkentry+0x14/0xc0 [xt_set]
        xt_check_match+0x238/0x260 [x_tables]
        __nft_match_init+0x160/0x180 [nft_compat]
 [..]
        sys_sendmsg+0x18/0x40
        linux_sparc_syscall+0x34/0x44
 other info that might help us debug this:
  Possible unsafe locking scenario:
        CPU0                    CPU1
        ----                    ----
   lock(&net->nft.commit_mutex);
                                lock(&table[i].mutex);
                                lock(&net->nft.commit_mutex);
   lock(&table[i].mutex);

Lockdep considers this an ABBA deadlock because the different nfnl subsys
mutexes reside in the same lockdep class, but this is a false positive.

CPU1 table[i] refers to the nftables subsys mutex, whereas CPU1 locks
the ipset subsys mutex.

Yi Che reported a similar lockdep splat, this time between ipset and
ctnetlink subsys mutexes.

Time to place them in distinct classes to avoid these warnings.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

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