lockd: fix swapped arguments in nlmsvc_match_ip()

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

lockd: fix swapped arguments in nlmsvc_match_ip()

When releasing locks by server IP address via /proc/fs/nfsd/unlock_ip,
nlmsvc_unlock_all_by_ip() calls nlm_traverse_files() with the server
sockaddr as the opaque @data argument:

nlm_traverse_files(server_addr, nlmsvc_match_ip, NULL);

The match callback is later invoked from nlm_traverse_locks() as:

match(lockhost, host);

where the first argument is the nlm_host that owns the lock, and the
second argument is the @data that was originally passed down (here the
server sockaddr). This is the convention every other match callback
relies on (nlmsvc_mark_host(), nlmsvc_same_host(), nlmsvc_is_client()):
arg1 is the real nlm_host, arg2 is the caller-supplied reference value.

nlmsvc_match_ip() has had these two arguments reversed ever since the
unlock-by-IP feature was introduced in commit 4373ea84c84d ("lockd:
unlock lockd locks associated with a given server ip"):

return rpc_cmp_addr(nlm_srcaddr(host), datap);

Here @host is actually the server sockaddr, so nlm_srcaddr(host)
dereferences a struct sockaddr as a struct nlm_host and reads garbage
at the offset of h_srcaddr; meanwhile @datap is actually the lock
owner's nlm_host but is compared as a sockaddr. As a result the
comparison practically never matches and locks are not released for the
requested IP.

Swap the arguments so the lock owner's source address is compared
against the requested server address:

return rpc_cmp_addr(nlm_srcaddr(datap), (struct sockaddr *)host);

[ cel: fix the misleading typedef parameter names too ]