Configure IPv6 DNS server using router advertisements.

- This work-in-progress commit simply adds a router
  solicitation write and advertisement read to the
  DNS configuration call as a proof of concept, and to
  demonstrate the startup delay imposed by the process.
- We need to figure out whether it's okay to make
  the container workload responsible for handling
  initial unavailability of DNS at startup. This
  would only occur when the workload has no IPv4
  network stack. If this is the case, we can just
  put the RA processing and DNS update in the
  background. Otherwise, we need to implement a
  method to conditionally delay workload startup
  when it's necessary to wait for the IPv6 resolver
  address.

Author: jglogan

Package.resolved

@@ -29,6 +29,7 @@ let package = Package(
         .library(name: "ContainerizationEXT4", targets: ["ContainerizationEXT4"]),
         .library(name: "ContainerizationOCI", targets: ["ContainerizationOCI"]),
         .library(name: "ContainerizationNetlink", targets: ["ContainerizationNetlink"]),
+        .library(name: "ContainerizationICMP", targets: ["ContainerizationICMP"]),
         .library(name: "ContainerizationIO", targets: ["ContainerizationIO"]),
         .library(name: "ContainerizationOS", targets: ["ContainerizationOS"]),
         .library(name: "ContainerizationExtras", targets: ["ContainerizationExtras"]),
@@ -196,6 +197,20 @@ let package = Package(
                 .product(name: "Crypto", package: "swift-crypto"),
             ]
         ),
+        .target(
+            name: "ContainerizationICMP",
+            dependencies: [
+                .product(name: "Logging", package: "swift-log"),
+                "ContainerizationExtras",
+            ]
+        ),
+        .testTarget(
+            name: "ContainerizationICMPTests",
+            dependencies: [
+                "ContainerizationExtras",
+                "ContainerizationICMP",
+            ]
+        ),
         .target(
             name: "ContainerizationNetlink",
             dependencies: [