Refactored obj.go to a more generic approach
Added object support for already implemented expressions
Added test for limit object
Fixes https://github.com/google/nftables/issues/253
Fix the marshall of the hash seed to be conditional, only if it is
explicitly set, we need to add it to the kernel as stated on the
libnftl and nftables projects.
Refence: https://git.netfilter.org/nftables/tree/src/netlink_linearize.c?id=25e7b99cc450490c38becb03d8bddd0199cfd3f9#n174
Otherwise, having a hash expression similar to this:
```
ip daddr set jhash tcp sport mod 2 seed 0x0 map { 0 : 192.168.0.1, 1 : 192.168.2.2 }
```
end up setting only the first IP and ignoring the second one.
Signed-off-by: Rafael Campos <methril@gmail.com>
turekt
Rafael Campos Las Heras
thediveo
Minaru