sstp: add ECDSA certs support and DH/ECDH config options

sstp: fix station_ids, add stat/snmp support & full crypto binding validation

sstp: allow custom http server response & other fixes

example function to use mac address as username:
function username(ses)
    return ses:hwaddr()
end

ipoe: pass mask to ifcfg in ip unnumbered mode

sstp: fix mppe, non-standard port and hostname checking issues

If the peer re-authenticates (because of option conf_interval) and pwdb
calls auth_result(), we may add the interval timer again to the session
context. This crashes accel-ppp when deleting the session, because the
interval timer is removed only once and the superfluous timers are
still running. Therefore, when removing the context, triton detects
this issue and calls abort().

To fix this, we need to detect if the session is already started and
just send a CHAP Success message in this case.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

When pwdb returns PWDB_NO_IMPL and chap_recv_response() performs the
authentication itself, it delegates this task to chap_check_response().
This function sends a CHAP Failure message if it can't retrieve the
password, but not in case of password mismatch. Since
chap_recv_response() already sends a CHAP Failure message on error,
the one sent by chap_check_response() is useless.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

When pwdb returns PWDB_NO_IMPL, then chap_recv_response() tries to
authenticate the peer itself. If this authentication succeeds but the
session is already started (in case of re-authentication, with option
conf_interval), no CHAP Success is sent.

This patch sends the missing CHAP Success message in this case, so that
the peer knows that its response has been received and accepted, and
that no retransmission is required.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>