Allow specification of which interfaces to bind to

[SphtKr]

In cases where the container has multiple interfaces/multiple IPs, it may be necessary to specify which interfaces Samba should use. In my case (microk8s+multus) it was listening additionally on a k8s-internal IP address and registering that IP address in DNS, which clients on the LAN would not be able to reach. This change allows specification of an environment variable BINDINTERFACES that becomes the interfaces value in smb.conf. The default is ${HOSTIP} lo which excluded any IPs other than the HOSTIP value.

This is a change from previous behavior, where all interfaces would be used, but this new behavior is probably desirable. The old behavior can be preserved by providing false explicitly in BINDINTERFACES.

[SphtKr]

Perhaps notably, I have added the interfaces options to the commands that join a DC to an existing domain, but the ${HOSTIP_OPTION} is not provided to those commands. I don't believe this breaks anything, but I wonder if the ${HOSTIP_OPTION} should be provided to those commands for a similar reason to the need for this PR's change.

[SphtKr]

it was listening additionally on a k8s-internal IP address and registering that IP address in DNS

One other comment--besides this, but any time the container was restarted it was likely to get a new (dynamic) internal IP, which would be added instead of replaced in DNS (I am using Bind9 though, which may be specific to this behavior)... so this was needed to stop proliferation of many unreachable IPs in DNS, not just one.