Fix SMB signing detection reporting "required" when only enabled

[ndog7]

The SMB detector read signing state from impacket's RequireSigning flag (and isSigningRequired(), which returns the same value). impacket force-sets RequireSigning=True for any SMB 3.1.1 session regardless of the server's actual security mode because 3.1.1 uses pre-auth integrity ("Always Sign"). Since Windows 10 / Server 2016+ negotiate 3.1.1 by default, hosts with signing merely enabled (a valid relay target) were misclassified as "signing required" and dropped as protected.

Fix: derive signing from the authoritative signal the SMB2_NEGOTIATE_SIGNING_REQUIRED bit in the server's negotiate-response SecurityMode via a new _get_signing_required() helper:

• SMB1 -> isSigningRequired() (accurate on the SMB1 path)

• SMB >= 3.0 -> test ServerSecurityMode & SMB2_NEGOTIATE_SIGNING_REQUIRED directly, bypassing impacket's 3.1.1 override

• SMB 2.0/2.1 -> RequireSigning (accurate; override doesn't apply and ServerSecurityMode isn't populated below 3.0)

  Changes (protocols/smb_detector.py):

• Add _get_signing_required(conn) helper encapsulating the logic above

• Route all four signing read sites through the helper:

  • main detection path
  • Kerberos-auth-failed fallback
  • logon-failure (STATUS_LOGON_FAILURE) fallback
  • access-denied (STATUS_ACCESS_DENIED) fallback

• Remove the now-unused per-site smbv1 = (dialect == SMB_DIALECT) locals