Enable options commonly needed by popular virtualization
and container applications. Use modules when possible to
avoid too much overhead for users not interested.

- add namespace and cgroup options needed
- add seccomp - optional, but enhances Qemu etc
- bridge, nat, veth, macvtap and multicast for routing
  guests and containers
- btfrs and overlayfs modules for container COW backends
- while near it, make fuse a module instead of built-in.

Generated with make saveconfig and dropping unrelated spurious
change hunks while commiting. bloat-o-meter old-vmlinux vmlinux:

add/remove: 905/390 grow/shrink: 767/229 up/down: 183513/-94861 (88652)
....
Total: Before=10515408, After=10604060, chg +0.84%
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>