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.