Exclude preferred/valid lifetime of 0 when comparing the minimal lifetime.

The functions getMinimalPreferredLifetime/getMinimalValidLifetime always
return 0 if any element has 0 lifetime, which results in a wrong expiry
of lifetime which is also 0 when scheduling the lease timer.

Bug: 260934173
Test: atest NetworkStackIntegrationTests
Test: atest NetworkStackTests
Change-Id: Idce90091457baaf4fd6b808323c5dc8e93b77462
2 files changed