In #5399 it was noticed, that IPC_Mode isn't being used within SystemV
IPC procedures, even though it was designed this way, which lead to a
weird API where in order to call SystemV IPC procedures multiple
transmutes and a bitwise-OR are needed.
This unifies IPC_Mode and IPC_Flags bitsets, making it possible to call
the SystemV IPC procedures without extra casts, and rearranges the flags
in a way that hopefully makes it easier to see when they are not
colliding and should not be mixed. The explanation, explaining this
arrangement of the enum was added.
The IPC_Perm structure is modified, so that the flags can be re-used
between the calls. It's probably not as good as keeping them separate,
but should work... hopefully.
Kept the "old" style of documentation for consistency.
Signed-off-by: Sunagatov Denis <thebumboni@gmail.com>