Fix missing line-feed for DHCPv6Client entry

Insertion of the DHCPv6Client causes subsequent systemd.network
entries to be parsed incorrectly. When a static address is configured
the "[Address]" section trails the DHCPv6Client line. The missing "\n"
prevents the static address from being honored.

Tested:
Assigned a static IPv4 address.
Prior to this commit the IPv4 address does not get assigned.
After applying this commit the static IPv4 address is assigned.

Change-Id: I416cba3d3b561baeab6d3ed88830602d9206fe86
Signed-off-by: Johnathan Mantey <johnathanx.mantey@intel.com>
diff --git a/src/ethernet_interface.cpp b/src/ethernet_interface.cpp
index 44f46f6..43a8ee0 100644
--- a/src/ethernet_interface.cpp
+++ b/src/ethernet_interface.cpp
@@ -1126,6 +1126,7 @@
     stream << "[IPv6AcceptRA]\n";
     stream << "DHCPv6Client=";
     stream << (dhcpIsEnabled(IP::Protocol::IPv6) ? "true" : "false");
+    stream << "\n";
 
     // Static IP addresses
     for (const auto& addr : addrs)