network_config: Enable [DHCP] option parameters by default
network_config: Enable [DHCP] option parameters by default

After factory reset, ethernet interfaces are set to DHCP as
expected. But the DNS and NTP servers are not requested.

This commit adds the [DHCP] options to the default network
file so that the DHCP REQUEST asks for the required options
from the DHCP server when fetching the fresh lease

Tested by:
 1. Factory reset the BMC and check if the DHCP request is sent
 for DNS and NTP etc
 2. Verify the default network file

Signed-off-by: sunharis <06d40626187f9f68f3926af1c7142bff884c1ed8@in.ibm.com>
Change-Id: I082694834a427400bfbfe2b2b0f871b0ecaee47b

openbmc/phosphor-networkd,openbmc/phosphor-networkd