…lobals

This commit removes compatibility with kernels 5.1 and older. From this point on,
Cilium relies on a read-only map to hold its datapath configuration data, and
config values will no longer be inlined into the bytecode.

This patch uses the new ebpf.VariableSpec abstraction for applying configuration
data to a CollectionSpec.

It also expands supported data types for runtime substitution to signed integers
and booleans, where before only unsigned integers were allowed.

Signed-off-by: Timo Beckers <[email protected]>

…NDEX

This is an example of converting a legacy preprocessor macro to a runtime configurable.

The default value of a configurable after declaring it with DECLARE_CONFIG() is zero,
so no need to assign dummy values.

Use ASSIGN_CONFIG to override the contents in tests after importing a declaration.

To avoid large refactors and churn, define e.g. THIS_INTERFACE_IFINDEX as a macro
around an accessor like CONFIG(interface_ifindex).

The section in TestWriteStaticData was removed because it only really checked whether
the logic in loader.ELFVariableSubstitutions roughly matches the one in cfg.writeStaticData,
which is of dubious benefit. A follow-up patch will remove ELFVariableSubstitutions,
so let's put it out of its misery instead of rejigging it even more.

Signed-off-by: Timo Beckers <[email protected]>