doc: Mention that veth.pair is ignored for unpriv

veth.pair is ignore for unprivileged containers as allowing an
unprivileged user to set a specific device name would allow them to
trigger actions in tools like NetworkManager or other uevent based
handlers that may react based on specific names or prefixes being used.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
doc: Add mention that veth.pair is ignored for unpriv in Japanese man

Update Japanese lxc.container.conf(5) for commit 8982c0f

Signed-off-by: KATOH Yasufumi <karma@jazz.email.ne.jp>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>