ipoe: include server's mac into weight notify packet to be used as additional key when weights are equal

new config options:
[ipoe]
weight=N - global weight
interface=ethX,weight=N - per-interface weight

How it works:
On reception of DHCPDISCOVER accel-ppp sends broadcast DHCP message to port 67 with same xid and add special vendor-specific option
where encodes its current session count multipled by weight.
On reception of such message accel-ppp searches session with same xid and compares weight.
If received weight is less than session's weight then it terminates this session.
per-interface weight=0 has special meaning as backup (fail-over) interface, f.e. it terminates session on any received weight.

By default weight based load balancing is disabled.
To enable need to specify global or/and per-interface weight.

Before this patch if agent-remote-id is not specified in config it get default value "accel-pppd".
Now if agent-remote-id is not specified then accel-ppp will not insert his Option 82 into relayed DHCP requests

Signed-off-by: NDmitry Kozlov <xeb@mail.ru>

Signed-off-by: NDmitry Kozlov <xeb@mail.ru>

This reverts commit cde7ee4d.

ipoe: implemented client address, router address and mask to be passed via radius