sosetup-network: bug when configuring management interface only

[dougburks]

When running sosetup-network and choosing to configure just a management interface (no sniffing interfaces), it looks like it automatically adds any non-management interfaces as sniffing interfaces but with no MTU. Empty MTU can cause the box to hang on boot.

Possible (untested) solution:
If user chooses to not configure any sniffing interfaces, then set MON_INTERFACES="" so that when we later run for INTERFACE in $MON_INTERFACES there is nothing for it to iterate over.

[dougburks]

commit:
Security-Onion-Solutions/securityonion-setup@0e2c071

[dougburks]

submitted for testing:
https://groups.google.com/d/topic/security-onion-testing/GSiD3QMv5OY/discussion

[dougburks]

published:
http://blog.securityonion.net/2016/08/securityonion-setup-20120912_24.html