Only pass ip[46].addr when _addrl contains a value

Submitted by:	crees
Reviewed by:	Mike Jakubik <mike.jakubik@intertainservices.com>
Approved by:	cperciva
MFC after:	2 weeks

etc/rc.d/jail

@@ -656,7 +656,8 @@ jail_start()
 		done
 
 		eval ${_setfib} jail -n ${_jail} ${_flags} -i -c path=${_rootdir} host.hostname=${_hostname} \
-			ip4.addr=\"${_addrl}\" ip6.addr=\"${_addr6l}\" ${_parameters} command=${_exec_start} > ${_tmp_jail} 2>&1 \
+			${_addrl:+ip4.addr=\"${_addrl}\"} ${_addr6l:+ip6.addr=\"${_addr6l}\"} \
+			${_parameters} command=${_exec_start} > ${_tmp_jail} 2>&1 \
 			</dev/null
 
 		if [ "$?" -eq 0 ] ; then