The default values of the "value_size" field is None. This can trigger
an issue
when computing the "len" field.

Test: str(EAP_MD5())

In order to fix this issue, the default value of the "value_size" field
has been set to 0.

Tests have been added in "regression.uts".

Added regression tests for EAP_TLS and EAP_FAST.

Use XStrLenField in EAP_MD5, EAP_TLS and EAP_FAST packets instead of StrLenField.

Delete blank lines before the class description (EAPOL, EAP, EAP_MD5, EAP_TLS and EAP_FAST packet classes).

"registered_options" dictionary was renamed "registered_methods"
(EAP-MD5, EAP-TLS etc are not options, but authentication methods).

EAP getlayer() and haslayer() methods have been overloaded in order to
allow access to a given "EAP layer" (such as EAP_TLS, for instance) by
providing the parent class name ("EAP"). For example, this is now
possible:

>>> eap_tls = EAP_TLS()
>>> EAP_TLS in eap_tls
True
>>> EAP in eap_tls
True
>>> eap_tls[EAP_TLS]
<EAP_TLS  |>
>>> eap_tls[EAP]
<EAP_TLS  |>

Regression tests have been added.

This should avoid random unrelated crashes.

NTPControl: rename field 'error' in 'err' in order to have the same name for the error field in NTP Control messages and NTP Private messages.

Use the XStrFixedLenField class which is now defined in scapy/fields.py + Fix typo.

* Improved main.py tests

* Small fixes

* Fix IA_PD length error

I tested this and noticed wireshark wasn't parsing the message correctly. Turns out the length is wrong.

* Update regression.uts

Fix test for DHCP6OptIA_PD

* Update length of DHCP6OptIA_PD in test.

This PR makes it possible to check if several flags are all set, by
writting, for example, `if pkt[TCP].flags.SA:`.

It only works for single letter flags (e.g., will work for TCP().flags
but not for IP().flags), and only when getting a value.

Thanks @guedou for suggesting that.

It is now possible to write `pkt[TCP].flags.S = True`.

This makes it possible to write `if pkt[TCP].flags.S: [...]`.