support limits for pps on ports

Observium already collect information about "all" ports.
And observium also collect pps statistics for unicast/broadcast/milticast traffic (ussually from IF-MIB).

I want to request new feature for this graph - discovery limits.

Usually on switches configured storm control, so the idea is to discovery that configuration.

What need to be improved:

• discovery for ports - os/model specific
• graph generation
• db structure for ports table
• alert checker for ports (support for using limit like @sensor_limit_low)
• other

 
Examples (random switch only for example):

• snmpwalk from D-Link DES-3028.
  Configuration was:

  # STORM

  config traffic trap none

  config traffic control 1-22 broadcast enable multicast enable unicast disable action shutdown threshold 64 countdown 5 time_interval 5

  config traffic control 23-28 broadcast disable multicast disable unicast disable action drop threshold 1000 countdown 0 time_interval 5

• snmpwalk from SNR S2995G

  snmpwalk ... SNR-SWITCH-MIB::portRateLimitTable

  SNR-SWITCH-MIB::portRateLimitPortIndex.4 = INTEGER: 4

  SNR-SWITCH-MIB::portRateLimitConfigBroadcastNum.4 = INTEGER: 645

  SNR-SWITCH-MIB::portRateLimitCurBroadcastNum.4 = INTEGER: 0

  SNR-SWITCH-MIB::portRateLimitConfigMulticastNum.4 = INTEGER: 500

  SNR-SWITCH-MIB::portRateLimitCurMulticastNum.4 = INTEGER: 0

  SNR-SWITCH-MIB::portRateLimitConfigUnicastNum.4 = INTEGER: 0

  SNR-SWITCH-MIB::portRateLimitCurUnicastNum.4 = INTEGER: 666

  SNR-SWITCH-MIB::portRateLimitConfigAllNum.4 = INTEGER: 0

  SNR-SWITCH-MIB::portRateLimitCurAllNum.4 = INTEGER: 666

  SNR-SWITCH-MIB::portRateLimitPacketsType.4 = INTEGER: 5

  SNR-SWITCH-MIB::portRateLimitViolationMode.4 = INTEGER: nocontrol(0)

  SNR-SWITCH-MIB::portRateLimitShutRecoveryTime.4 = INTEGER: 300

  configuration was:

  Interface Ethernet1/0/4

  ...

  rate-violation broadcast 645

  rate-violation multicast 500

  ...