add script to automatically enroll tap device into bridge

bhyve/enroll-tap.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+
+bridge=$1
+tap=$2
+
+while true; do
+  ifconfig $tap
+  if [ $? -eq 0 ]; then
+    ifconfig $bridge addm $tap
+    break
+  fi
+
+  sleep 1
+done