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.

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

 Simplify previous commit, if 4th field isn't empty and doesn't
 start with reserved chars (*-!), assume it as pool name.
 Also, fix build warn without OPENSSL.

 Chap-secrets' ipdb uses 4th field as static peer ipv4 address. With no radius
 and multiple same username sessions, it's impossible to use non-default pool
 for such sessions.
 Abuse chap-secret's 4th field as pool=name to specify session's pool name.
 With ippool module loaded after chap-secrets (default order), it will be
 used for allocation from the specified poll name.

 Compatibility considerations:
 * pppd will skip 'pool=*' with warn 'unknown host in auth. address list'
   same as 5th field - shaper, because starting from 4th field pppd
   parse list of value. so, no new effects here.
 * previous versions of accel-ppp will parse 'pool=*' as empty address.
 * with no 'pool=*' in chap-secrets or with no chap-secrets loaded, no
   behavior change.
 * with no ippool loaded, session will get no peer address.
 * with ippool loaded before chap-secrets, chap-secrets's ipdb will not
   be used, therefore neither ip addess not pool name will has no effect.
 * if chap-secrets' pool is invalid or not found, default pool will be
   used by ippool or address came from radius.
 * chap-secret's pool name might override pool came from radius, if
   radius module is loaded after chap-secrets and no address came from
   radius.

 Reuse exsisting radius functionality and allow set iterface name
 template for pppoe/pptp/l2tp, '%d' specification will be replaced
 automagically to the next available index by kernel.
 PPP interface rename allows to easy differ client's interfaces from
 the other ppp ones, for example, with just netfilter interface rules.

 Example:
  [pptp]
  ifname=pptp%d will produce pptp0, pptp1, ...

 With incoming l2tp hello there's no need to ask peer for
 replies in configured hello-interval, so just postpone it.
 Helps against false-positive echo failures with heavily
 loaded channels and/or peers.

 With incoming pptp echo request there's no need to ask
 peer for replies in configured echo-interval, so just
 postpone it. Helps against false-positive echo failures
 with heavily loaded channels and/or peers.

 Sent echos counter is overloaded with random icmp id, so
 echo-failure setting is either ignored or causes random pptp
 channel stops within valid accumulated fail count range, i.e
 on the the first fail. Since icmp id is not actually used for
 checking, fix issue by dropping overload.
 Default echo-failure value is 3, so allow endless echo fails
 without channel drop by setting echo-failure to 0.

 After session is freed on our end, kernel doesn't bother with possible
 incoming data packets and just passes them to userspace, in turn
 they are mistreated as short control packets with corresponding errors.
 Since there's no special data packet handling, just ignore them.

 non-/64 subnets still needs Router Advertimenets for the
 default route & RDNSS.

Assign opt82_ses=ses if shared=0