[settings] skip non-volatile save with same NetworkInfo/ParentInfo (#3552)
[settings] skip non-volatile save with same NetworkInfo/ParentInfo (#3552)

This commit adds new check in `settings.cpp` for saving of
`NetworkInfo` and `ParentInfo` in non-volatile memory to verify that
the new value is different from previously saved content. This reduces
number of writes after a device reboot.
lanyuwen/openthread,jwhui/openthread,jwhui/openthread,turon/openthread,lanyuwen/openthread,bukepo/openthread,abtink/openthread,bukepo/openthread,librasungirl/openthread,abtink/openthread,srickardti/openthread,srickardti/openthread,bukepo/openthread,lanyuwen/openthread,srickardti/openthread,lanyuwen/openthread,chshu/openthread,bukepo/openthread,openthread/openthread,librasungirl/openthread,turon/openthread,chshu/openthread,jwhui/openthread,abtink/openthread,librasungirl/openthread,lanyuwen/openthread,chshu/openthread,abtink/openthread,openthread/openthread,openthread/openthread,chshu/openthread,chshu/openthread,turon/openthread,turon/openthread,openthread/openthread,chshu/openthread,librasungirl/openthread,jwhui/openthread,lanyuwen/openthread,srickardti/openthread