The current implementation of `CanUseIPVSProxier()` reads `/proc/modules`
to check whether IPVS related kernel modules can be loaded.
You might get a false-negative when the kernel modules are installed to
the system but haven't been loaded into the kernel.
This patch firstly try to run `modprobe` to load specified kernel
modules, then just log warnings if error occured.
Secondly, it will check loaded kernel modules by reading
`/proc/modules`, return an error if any required module is missing.
This change will not break the compatability of existing implementation.
Running kube-proxy in a container without mounting `/lib/modules` will
cause `modprobe` warnings, but not raise an error if all required modules are
present in the host kernel.
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