kernel-pfkey: Report packet counts of IPsec SAs

Seems that packet counts can be retrieved after all. At least the Linux
and FreeBSD kernels treat the number of allocations as number of packets.
We actually installed packet limits in that field already.

src/libhydra/plugins/kernel_pfkey/kernel_pfkey_ipsec.c

@@ -1978,8 +1978,8 @@ METHOD(kernel_ipsec_t, query_sa, status_t,
 	}
 	if (packets)
 	{
-		/* not supported by PF_KEY */
-		*packets = 0;
+		/* at least on Linux and FreeBSD this contains the number of packets */
+		*packets = response.lft_current->sadb_lifetime_allocations;
 	}
 	if (time)
 	{