libxt_policy: cannot set spi/reqid numbers higher than 0x7fffffff

libxt_policy: cannot set spi/reqid numbers higher than 0x7fffffff

http://bugzilla.netfilter.org/show_bug.cgi?id=577

When using the -m policy match, the option argument for --spi is converted
using strtol(), which returns a signed 32 bit value, so the highest
positive value is 0x7fffffff. Instead strtoul() should be used.
The same applies for the --reqid option argument.

Signed-off-by: Patrick McHardy <kaber@trash.net>