[NETFILTER]: Use __u32 in struct nf_inet_addr

As reported by David Woodhouse <dwmw2@infradead.org>, using u_int32_t
in struct nf_inet_addr breaks the busybox build. Fix by using __u32.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>