Fix IPv6 support on Windows

EAP_MD5 class added.

Updates the CDP module (scapy/contrib/cdp.py).

Fix empty LLTDAttribute build & dissect

  - LLTDAttribute() produces a Raw instance (or crashes, when
    conf.debug_dissector is set).

  - str(LLTDAttribute(type=18)) crashes.

New defrag() test

Test send / sendp and sniff

Thanks @gpotter2

layers/inet6/routes: fix ndp resolution without default route

Add a tcpdump-based L2listen socket

Sending a IPv6 packet without Ether.dst mac defined fails when there is
not default IPv6 route defined with the following message:

WARNING: No route found for IPv6 destination fd00:200::1 (no default route?)

Because, when there is no default IPv6 route defined, conf.iface6 is
initialized to the loopback interface and the conf.route6.route() method
is called with dev=conf.iface6.

According to the docstring of conf.route6.route():

  if optional 'dev' parameter is provided a specific interface,
  filtering is performed to limit search to route associated to
  that interface.

This will result in the system never finding on which interface it
should send a NDP packet.

Do not call conf.route6.route() with dev=conf.iface6.

Signed-off-by: Samuel Gauthier <samuel.gauthier@6wind.com>
Signed-off-by: Robin Jarry <robin.jarry@6wind.com>

[Windows/Small fix] Add missing stop_filter

Removed outdated readfunc fonction

[Windows] Tiny fix to show error when interface does not exist

Switch from PyCrypto to Cryptography

This also includes some fixes for tcpdump()

Pypy won't run crypto tests on Travis CI because the cryptography
module cannot be installed with the Pypy version used.

See
  - https://github.com/pyca/cryptography/issues/2968 (discussion)
  - https://github.com/pyca/cryptography/issues/1141 (older)

Signed-off-by: Thomas Faivre <thomas.faivre@6wind.com>

Change the cryptographic library used in the following layers:
 * IPSec
 * TLS
 * Dot11

Notes:
 * Fix the WEP key in regression.uts: Should be a 40 bits key (5 ASCII)
   and 24 bits nonce for 64 bits WEP. The key was 8 ASCII => 88 bits
   in total
 * AES-GCM and AES-CMAC algorithms are now native in cryptography: add
   tests in ipsec.uts
 * cryptography only supports Python 2.6+
 * Fix the docstring for the pad method

Removed:
 * MD2 and MD4 hash algorithms for RSA in tls/crypto/pkcs1.py
 * AES-XCBC-96 not supported by cryptography.

Signed-off-by: Thomas Faivre <thomas.faivre@6wind.com>

The urandom function from the os package is a better RNG function than
the PyCrypto's Random.

Signed-off-by: Thomas Faivre <thomas.faivre@6wind.com>

Signed-off-by: Thomas Faivre <thomas.faivre@6wind.com>

[coverage] codecov appveyor support

Get constant values from "consts" since it is no longer in arch

Fix ls(): fix layer names and handle tuple default values (test added)