Rework namespace functions and types

[rusty-snake]

Successor of #1402

• Add set_namespace function.
• Deprecate move_into_link_name_space and move_into_thread_name_spaces functions.
• Add NamespaceType.
• Deprecate ThreadNameSpaceType and LinkNameSpaceType.
• Add nsfs ioctls.
• Add NoArgGetter ioctl pattern.

Not yet in the PR:

• NS_GET_PID_FROM_PIDNS
• NS_GET_TGID_FROM_PIDNS
• NS_GET_PID_IN_PIDNS
• NS_GET_TGID_IN_PIDNS
• Merged: https://github.com/rust-lang/libc/pull/4436
• Released: libc 0.2.174