Fixed keepalive to send ping request only when host mode is client

Fixed keepalive to send ping request only when host mode is client

ping message should be sent when host mode is client

Change-Id: I2ac94e1340c1607969391b86577b9101ddc013b5
Signed-off-by: hyuna0213.jo <hyuna0213.jo@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/15675
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>
Reviewed-by: Jaehong Jo <jaehong.jo@samsung.com>
Reviewed-by: Ashok Babu Channa <ashok.channa@samsung.com>