Fix a possible segmentation fault of ExpiryTimer.

Fix a possible segmentation fault of ExpiryTimer.

The thread for ExpiryTimer might be started before members are initialized.

Change-Id: I2d83a60bb84422e033f6165aef3cb0136edbeae7
Signed-off-by: coderhyme <jhyo.kim@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/3187
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Madan Lanka <lanka.madan@samsung.com>
(cherry picked from commit 735bf9c001146666d86f5e744e3a0cce6a5aa860)
Reviewed-on: https://gerrit.iotivity.org/gerrit/3197