chore(aws-ec2): add ICMPv6 protocol method

This allows creation of a security group rule that permits
ICMPv6.

packages/@aws-cdk/aws-ec2/README.md

@@ -529,11 +529,14 @@ the connection specifier:
 ec2.Port.tcp(80)
 ec2.Port.tcpRange(60000, 65535)
 ec2.Port.allTcp()
+ec2.Port.allIcmp()
+ec2.Port.allIcmpV6()
 ec2.Port.allTraffic()
 ```
 
-> NOTE: This set is not complete yet; for example, there is no library support for ICMP at the moment.
-> However, you can write your own classes to implement those.
+> NOTE: Not all protocols have corresponding helper methods. In the absence of a helper method,
+> you can instantiate `Port` yourself with your own settings. You are also welcome to contribute
+> new helper methods.
 
 ### Default Ports
 

packages/@aws-cdk/aws-ec2/lib/port.ts

@@ -304,6 +304,18 @@ export class Port {
     });
   }
 
+  /**
+   * All ICMPv6 traffic
+   */
+  public static allIcmpV6() {
+    return new Port({
+      protocol: Protocol.ICMPV6,
+      fromPort: -1,
+      toPort: -1,
+      stringRepresentation: 'ALL ICMPv6',
+    });
+  }
+
   /**
    * All traffic
    */

packages/@aws-cdk/aws-ec2/test/port.test.ts

@@ -0,0 +1,16 @@
+import { Port, Protocol } from '../lib';
+
+describe('port', () => {
+  describe('Port class', () => {
+    describe('.allIcmpV6', () => {
+      it('returns expected instance of Port', () => {
+        expect(Port.allIcmpV6()).toEqual(new Port({
+          protocol: Protocol.ICMPV6,
+          fromPort: -1,
+          toPort: -1,
+          stringRepresentation: 'ALL ICMPv6',
+        }));
+      });
+    });
+  });
+});