builder/flatcar: Drop requirement to provide '-flatcar' after kernel …

…version

This was an arbitrary requirement that served no purpose. Kernel-crawler
generates configs with the kernelrelease set to the Flatcar version number
without the '-flatcar' suffix, so let's be consistent with that.

Signed-off-by: Jeremi Piotrowski <jpiotrowski@microsoft.com>

README.md

@@ -170,11 +170,12 @@ driverversion: master
 ```
 
 ### flatcar
+
 Example configuration file to build both the Kernel module and eBPF probe for Flatcar.
-The Flatcar release version needs to be provided in the `kernelrelease` field and must be followed by `-flatcar`.
+The Flatcar release version needs to be provided in the `kernelrelease` field instead of the kernel version.
 
 ```yaml
-kernelrelease: 3185.0.0-flatcar
+kernelrelease: 3185.0.0
 target: flatcar
 output:
   module: /tmp/falco-flatcar-3185.0.0.ko

pkg/driverbuilder/builder/flatcar.go

@@ -32,7 +32,7 @@ func (c flatcar) Script(cfg Config) (string, error) {
 	}
 
 	kr := kernelrelease.FromString(cfg.Build.KernelRelease)
-	if kr.Extraversion != "flatcar" {
+	if kr.Extraversion != "" {
 		return "", fmt.Errorf("unexpected extraversion: %s", kr.Extraversion)
 	}