Allow starting jails with ip[46] set to inherit

Either or both ip4 and ip6 can be set to inherit. For example I have used the
following config:

```
  interface = vtnet0;
  ip4 = inherit;
  ip6 = new;
  ip6.addr = 2a01:xxxx:xxxx:xxx::1;
```

usr/local/share/bastille/start.sh

@@ -35,6 +35,21 @@ usage() {
  error_exit "Usage: bastille start TARGET"
 }
 
+# indicate if an IP configurtaion value (e.g. a value given for ip4 or ip6)
+# requires extra configuration external to the jail
+#
+# success if it does, failure if it does not
+ip_require_config() {
+
+ case "${1}" in
+ disable|inherit|"not set")
+ return 1
+ ;;
+ esac
+
+ return 0
+}
+
 # Handle special-case commands first.
 case "$1" in
 help|-h|--help)
@@ -69,14 +84,18 @@ for _jail in ${JAILS}; do
 
  ## test if not running
  elif [ ! "$(/usr/sbin/jls name | awk "/^${_jail}$/")" ]; then
- # Verify that the configured interface exists. -- cwells
- if [ "$(bastille config $_jail get vnet)" != 'enabled' ]; then
- _interface=$(bastille config $_jail get interface)
- if ! ifconfig | grep "^${_interface}:" >/dev/null; then
- error_notify "Error: ${_interface} interface does not exist."
- continue
+ ## if networking is entirely inherited we can skip any setup
+ _ip4=$(bastille config $_jail get ip4)
+ _ip6=$(bastille config $_jail get ip6)
+ if ip_require_config "${_ip4}" || ip_require_config "${_ip6}"; then
+ # Verify that the configured interface exists. -- cwells
+ if [ "$(bastille config $_jail get vnet)" != 'enabled' ]; then
+ _interface=$(bastille config $_jail get interface)
+ if ! ifconfig | grep "^${_interface}:" >/dev/null; then
+ error_notify "Error: ${_interface} interface does not exist."
+ continue
+ fi
  fi
- fi
 
  ## warn if matching configured (but not online) ip4.addr, ignore if there's no ip4.addr entry
  ip=$(bastille config "${_jail}" get ip4.addr)