Fix panics when using iif or oif with ip rule

[dxfgg17]

Copying string s (which size is n) in buffer of size n+1 always panics because rust expect two slices of same length.

Since buffer has been initialized with 0, no need to add a second instruction like : buffer[s.len()+1] = 0;.

[dxfgg17]

Sorry for the mistake and thank you for your review. I fixed the issue :)

[cathay4t]

Merged. Thanks!