TODO: accounting/statistics, minimize syscall & memory usage

triton: fix crash due gcc mis-optimization of alloca()

 since alloca() result is used indirectly, gcc 4.7.2 thinks
 the whole call can be dropped on any optimization level.

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.

Introduced 4 priorities:
0 - management (cli)
1 - starting sessions (default priority)
2 - active sessions
3 - finishing sessions

If prefix length is 128 then send RA with 64 prefix length and add point-to-point ipv6 address on interface

If pool specified with /128 prefix length, then initialize intf_id by gw_ip6_address and peer_intf_id by generated pool address.

ppp: fix interface rename if kernel returns not zero, but picked index

config changes:
[ip-pool]
x.x.x.x/mask,name=pool1
y.y.y.y/mask,name=pool2,next=pool1

chap-secrets: add pool name support