libiptc: fix wrong maptype of base chain counters on restore

libiptc: fix wrong maptype of base chain counters on restore

When a ruleset that does not reset any chain policies/counters, such as

	*filter
	COMMIT

is sourced by iptables-restore, the previous policy and counters
(i.e. the ones read from the kernel) are reused. The counter skew
offsetting is wrong however, causing the read value to be readded to
the kernel value. This manifests itself in practice by the counter
value almost doubling everytime iptables-restore is called.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>