Make CONFIG_NET and CONFIG_SECCOMP_FILTER independent of CONFIG_NET

[Norbert Manthey]

Dear all,

currently, KVM and SECCOMP rely on functionality of CONFIG_NET, and hence the
latter has to be enabled when building the kernel for the first two
configurations. However, there exists scenarios where the system does not need
networking, but KVM and SECCOMP filters. To reduce the kernel image size for
these scenarios, and to be able to drop active code, this commit series allows
to enable CONFIG_KVM and CONFIG_SECCOMP_FILTER without using CONFIG_NET.

The functionality that is required for seccomp filters is kept in the same
files and - after reordering the source code - is guarded with a single ifdef
per file.

I hope these changes are useful for other scenarios than the one I currently
face.

Best,
Norbert

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