net: ipv6: Return the prefix lifetime in seconds
net: ipv6: Return the prefix lifetime in seconds

Use the proper API to get the remaining time in prefix timer
and return the value in seconds as expected.

Change-Id: I055ce0ba6092c23ad60d6775ce75a0a67ad91d26
Signed-off-by: Jukka Rissanen <f9f077d1da4c7aa947f9864fa5a28c3588f6a45d@linux.intel.com>

fbsder/zephyr,fbsder/zephyr,fbsder/zephyr,fbsder/zephyr,fbsder/zephyr