ITL: Implement inverse switch for snmp_interface CheckCommand

As for Interface Monitoring it is sometime needed to inverse the status (down -> OK, up -> NOT OK).

Can be configured via snmp_interface_inverse variable (boolean).

fixes #115

Signed-off-by: Michael Friedrich <michael.friedrich@icinga.com>

AUTHORS

@@ -120,6 +120,7 @@ Steve McMaster <mcmaster@hurricanelabs.com>
 Thomas Gelf <thomas@gelf.net>
 Thomas Widhalm <thomas.widhalm@icinga.com>
 Tim Hardeck <thardeck@suse.de>
+Tim Weippert <weiti@weiti.eu>
 Timo Buhrmester <van.fstd@gmail.com>
 Tobias Birnbaum <osterd@gmx.de>
 Tobias von der Krone <tobias.vonderkrone@profitbricks.com>

doc/10-icinga-template-library.md

@@ -1895,6 +1895,7 @@ snmp_privpass               | **Required.** SNMP version 3 priv password. No val
 snmp_warn                   | **Optional.** The warning threshold.
 snmp_crit                   | **Optional.** The critical threshold.
 snmp_interface              | **Optional.** Network interface name. Default to regex "eth0".
+snmp_interface_inverse      | **Optional.** Inverse Interface check, down is ok. Defaults to false as it is missing.
 snmp_interface_perf         | **Optional.** Check the input/ouput bandwidth of the interface. Defaults to true.
 snmp_interface_label        | **Optional.** Add label before speed in output: in=, out=, errors-out=, etc.
 snmp_interface_bits_bytes   | **Optional.** Output performance data in bits/s or Bytes/s. **Depends** on snmp_interface_kbits set to true. Defaults to true.

itl/command-plugins-manubulon.conf

@@ -183,6 +183,9 @@ object CheckCommand "snmp-interface" {
 		"-e" = {
 			set_if = "$snmp_interface_errors$"
 		}
+		"-i" = {
+			set_if = "$snmp_interface_inverse$"
+		}
 		"-r" = {
 			set_if = "$snmp_interface_noregexp$"
 		}