Since #116 implemented fragile comparisons of iptables rules to avoid
calling the iptables binary excessively during every reconciliation, the
iptables rules for IPIP encapsulation must be updated to match the
expected output. One complication is that rather than returning the
protocol number in the rule, iptables resolves the protocol number to a
name by looking up the number in the netd protocols database. This name
can vary depending on the host's environment. This commit adds two
solutions for resolving the protocol name:
1. a fixed mapping to the string `ipencap`, which should always work
for Kilo whenever it runs in the Alpine Linux container; and
2. a runtime lookup using the netd database, which only works if Kilo is
compiled with CGO and is meant to be used only if Kilo is not running in
the normal container environment.
Signed-off-by: Lucas Servén Marín <lserven@gmail.com>
