v7.1 stable AGNi for MIATOLL excalibur/curtana/joyeuse/gram

selinux: reduce calls to context_struct_to_string().
selinux: use stack on security_sid_to_context() if possible.
config: enable System V IPC, mqueues, and PID namespaces.
media: v4l2-ioctl: Use larger on-stack video copy buffers.
xattr: Avoid dynamically allocating memory in getxattr.
ext4: Avoid dynamically allocating memory in ext4_ext_remove_space.
dcache: increase DNAME_INLINE_LEN.
seq_file: allocate seq_file from kmem_cache.
diag: Add timer to make sure wakelock no stuck.
dm-crypt: increase threads.
cpu-boot changes & more.