cmd/bpf2go: read more flags from environment

[Puqns67]

No description provided.

[ti-mo]

Thanks for the patch! Left a small nit, and would like @lmb's sign-off on this as well.

[lmb]

Left some questions. Could you extend the unit tests in main_test.go to cover the new variables?

[lmb]

This error should be surfaced to the user, otherwise incorrect settings like NO_STRIP=gobbledigook will silently disable stripping.

[Puqns67]

This error should be surfaced to the user, otherwise incorrect settings like NO_STRIP=gobbledigook will silently disable stripping.

I made some of these changes, what do you think?

Suggested change

	result, _ := strconv.ParseBool(val)
	result, err := strconv.ParseBool(val)
	if err != nil {
	fmt.Fprintf(os.Stderr, "Warning: The value '%s' passed from environment variable '%s' is undefined in strconv.ParseBool, using default value (%t).\n", val, key, defaultVal)
	return defaultVal
	}

What else should I change?
Do I need to use b2g.stdout instead of os.Stderr? (Need to add a parameter to pass writer)

[lmb]

A warning is nice, what about just returning the error from the function instead? That means you need to add a separate block to add it to run() but that isn't so bad in my opinion.