Server hangup after long unresponsive callback

[GiedriusM]

Restserver became unresponsive after NodeRed (lesley) re-deploy. As seen from the log, server tried to send notifications to callback service, but froze in it for several minutes (maybe node.js express server was partially closed/closing?). After completion (or failure) it briefly processed pending events but neither CoAP, nor REST service is accessible anymore.

Aug 30 10:01:08 raspberrypi REST[14672]: [CALLBACK] Sending to http://192.168.100.58:5728/notification
Aug 30 10:01:08 raspberrypi REST[14672]: [MONITOR] Client 1 updated.
Aug 30 10:01:08 raspberrypi REST[14672]:         name: 'urn:uuid:c9d15fe9-5570-40e0-84d2-db68ef960e83'
Aug 30 10:01:08 raspberrypi REST[14672]:         bind: 'UQ'
Aug 30 10:01:08 raspberrypi REST[14672]:         lifetime: 16
Aug 30 10:01:08 raspberrypi REST[14672]:         objects: /3301/0, /3313/0, /3314/0, /3315/2, /3327/2, /3334/0, /3341/0,
Aug 30 10:01:08 raspberrypi REST[14672]: [CALLBACK] Sending to http://192.168.100.58:5728/notification
Aug 30 10:13:27 raspberrypi REST[14672]: [OBSERVE-RESPONSE] id=1535621712#dd91997e-5125-035f-4a73-1579 count=11478469 data=0x7ee0a5d4
.....
Aug 30 10:13:27 raspberrypi REST[14672]: [SSDP] Request from [fd30:db7c:6394:0:592c:ef27:cab2:b619]:1900 len=112
Aug 30 10:13:27 raspberrypi REST[14672]: ----------
Aug 30 10:13:27 raspberrypi REST[14672]: M-SEARCH * HTTP/1.1
Aug 30 10:13:27 raspberrypi REST[14672]: HOST: [FF05::C]:1900
Aug 30 10:13:27 raspberrypi REST[14672]: MAN: "ssdp:discover"
Aug 30 10:13:27 raspberrypi REST[14672]: MX: 1
Aug 30 10:13:27 raspberrypi REST[14672]: ST: urn:8devices-com:service:lwm2m:1
Aug 30 10:13:27 raspberrypi REST[14672]: [1B blob data]
Aug 30 10:13:27 raspberrypi REST[14672]: ----------
// COAP AND LWM2M UNREACHABLE

rest.log

Related to #44