Replace '.' with '/' on sysctl interface names

[jcaamano]

No description provided.

[maiqueb]

Why is this change needed ? What error do you see without this change ?

I'm specifically interested in why macvlan (where we've 'looted' this from) does not require it, check its implementation here.

[jcaamano]

From http://man7.org/linux/man-pages/man5/sysctl.d.5.html

Note that either "/" or "." may be used as separators within sysctl
variable names. If the first separator is a slash, remaining slashes
and dots are left intact. If the first separator is a dot, dots and
slashes are interchanged. "kernel.domainname=foo" and
"kernel/domainname=foo" are equivalent and will cause "foo" to be
written to /proc/sys/kernel/domainname. Either
"net.ipv4.conf.enp3s0/200.forwarding" or
"net/ipv4/conf/enp3s0.200/forwarding" may be used to refer to
/proc/sys/net/ipv4/conf/enp3s0.200/forwarding.

If you get an interface name from DeviceID such as eth0.1, the correct key to use under sysctl is net.ipv4.conf.eth0/1... or net/ipv4/conf/eth0.1.... Otherwise you get an error such as /proc/sys/net.ipv4.conf.eth0/1... not found

sysctl package also needs fixing: containernetworking/plugins#437

macvlan cni does not need it because it is not using interface names that include dots at that time.