check_snmp_int.pl new options

[phsm]

Added two new options to check_snmp_int.pl, which allow to exclude from monitoring interfaces by the following criteria:
--ign-admindown: Ignore interfaces in Admin down state
--ign-emptyalias: Ignore interfaces having empty alias (port description)

Also, fixed the warning like:
Use of uninitialized value $speed_real in concatenation (.) or string at ./check_snmp_int_new.pl line 979
wheb the interface speed is not set (e.g. port transceiver is absent).

[waja]

While I personally dislike that here are two different scopes are smashed into one PR, I'm interested into the option to ignore interfaces that are admin down.
@dnsmichi maybe you can consider f9d6415 here? I'm actually preparing a new package for Debian trying to get things done before the feature freeze is keeping changes impossible.

[dnsmichi]

I'm busy as always, and don't have time to test things in here in the next coming months. That's why I've added the note onto this project not being actively maintained anymore.

If you provide me a list of PRs where I can click "merge" without further objections, I can do that in 5 minutes. If you consider just one of the commits here, please fork the repo and cherry-pick the single commit into a new PR.

[phsm]

If you want, I can split my PR for a 3 different ones:

• add --ign-admindown option
• add --ign-emptyalias option
• fix the warning

[SteScho]

Thanks for your work, added PR 60. Please create a new PR if something is missing.