Wlan trap restrain by severity.
critical: means the trap whose severity is not higner than critical will not be sent.
major: means the trap whose severity is not higner than major will not be sent.
minor: means the trap whose severity is not higner than minor will not be sent.
warning: means the trap whose severity is not higner than warning will not be sent.
none: means all the severities of traps can be sent.