headers: Big rework

 - every header must not be sensitive in which order it's
   included into the source file

 - in some headers we use tabs aligned members, in some -- not,
   unify it

 - declare routines in headers as external, especially in uapi

 - provide arguments names in header function declarations

Now it's a way simplier to include headers when develop new
C file.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>