net: lwm2m: Improve thread safety of the library #140720

Job	Run time
twister-build-prep	4m 0s
twister-build (1)	40m 29s
twister-build (2)	1h 3m 37s
twister-build (3)	27m 39s
twister-build (4)	31m 53s
twister-build (5)	42m 31s
twister-build (6)	26m 48s
twister-build (7)	18m 45s
twister-build (8)	42m 45s
twister-build (9)	28m 55s
Publish Unit Tests Results	11s
Check Twister Status / all jobs passed	1s
	5h 27m 34s

Provide feedback