implemented connlimit module which can be used to reduce system overload due to flood of connections

l2tp: add Vendor-Name attribute to SCCRP

* implemented named IP pools (radius Framed-Pool attribute)
* implemented logging to system logger (log_syslog)
* implemented ability to send cli commands via snmp
* implemented PADI limiting (pppoe)
* implemented simultaneous radius requests limiting
* various bug fixes and improvements

This reverts commit ee41cba6.