Update both the enableIPsecIPv4 and 6 methods to utilize the helper
methods introduced in the previous commit.

Signed-off-by: Louis DeLosSantos <louis.delos@isovalent.com>

Prior to this commit the XFRM state and policy creation code would both
explicitly create XFRM FWD rules and implicitly (done during policy-in
creation).

This commit disambiguates where FWD policies are created. We opt to
always make them explicit. This will help with refactoring efforts in
a subsequent commit.

After this commit all FWD rules are created within the same function
that IN and OUT policies are created as well. We also add a new IPSecDir
constant to explicitly instruct the control plane to create a forward
rule.

Signed-off-by: Louis DeLosSantos <louis.delos@isovalent.com>

This commit introduces a new structure for declarative declaration of an
XFRM Policy and State.

This structure provides a consistent set of fields which are required
for creating an XFRM state and its associated policies.

Having a well defined structure allows us to declare exactly how an XFRM
policy should look at a higher level, and methods which are passed this
structure are in charge of creating the policy as the structure defines.

Signed-off-by: Louis DeLosSantos <louis.delos@isovalent.com>

This commit updates the methods which create XFRM states and policies to
use the declarative structure introduced in the previous commit.

Each policy is now well-defined before passing the declarative structure
down to the methods which do the heavy lifting of policy creation.

The heavy-lifting structures no longer impose a constraint on how/what
arguments are provided and instead refer to the declarative
IPSecParameter structure for the information they need.

This allows the developer to reason about the XFRM state and policy they
are creating at a higher level, and in one place.

Signed-off-by: Louis DeLosSantos <louis.delos@isovalent.com>

This function will be replaced by individual tests for IN, FWD, and OUT
policy creationg in the following commit.

Signed-off-by: Louis DeLosSantos <louis.delos@isovalent.com>

This commit introduces 3 new tests for specifically testing the creation
of XFRM states and policies in a particular direction, using the
declarative IPSecParamater struct.

Additionally, existing tests are updated to utilize the structure.

Signed-off-by: Louis DeLosSantos <louis.delos@isovalent.com>

Remove the use of IPSecDirBoth for creating both IN and OUT policies.

This option was only used in tests and had no functional use during
Cilium's runtime.

Signed-off-by: Louis DeLosSantos <louis.delos@isovalent.com>