dhcpd: Merge in DHCP options from the orignal offer

We've found that some APs respond to DHCP REQUEST messages with a
subset of the DHCP options that were present in the original DHCP
negotiation.  Copy such options out of the stored lease and carry
them forward whenever a lease renewal succeeds.

BUG=chromium:360452
TEST=New test network_DhcpRenewWithOptionSubset, CL:195268

Change-Id: If2edad471899b142b3c20ac26fbccc350e82005a
Reviewed-on: https://chromium-review.googlesource.com/195270
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Queue: Paul Stewart <pstew@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
4 files changed