[NET]: Fix permissions of /proc/net

commit e9720acd

 ([NET]: Make /proc/net a symlink on /proc/self/net (v3))
broke ganglia and probably other applications that read /proc/net/dev.

This is due to the change of permissions of /proc/net that was
introduced in that commit.

Before: dr-xr-xr-x 5 root root 0 Mar 19 11:30 /proc/net
After: dr-xr--r-- 5 root root 0 Mar 19 11:29 /proc/self/net

This patch restores the permissions to the old value which makes
ganglia happy again.

Pavel Emelyanov says:

	This also broke the postfix, as it was reported in bug #10286
	and described in detail by Benjamin.

Signed-off-by: Andre Noll <maan@systemlinux.org>
Acked-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>