Refactor out the IPv4-only provisioning result verification.

So far the provisioning verification is included inside handleDhcpPacket
and follows DHCP handshake, which works for IPv4-only provisioning, but
when IPv6 stack is also enabled in some tests, then IPv6 link-local
address will be configured automatically when interface is up. Refactor
out the IPv4 provisioning function, then it's flexible to verify something
else we are interested in (e.g. IPv6 link-local, privacy addresses).

Bug: 131781810
Test: atest NetworkStackIntegrationTests NetworkStackNextIntegrationTests
Merged-In: I7f5aba2d19de9bdbd0962bc3268d51c19112d9d2
Change-Id: I7f5aba2d19de9bdbd0962bc3268d51c19112d9d2