libsmb,s3/smbd: dump SMB3+ session keys if debug parm is set

libsmb,s3/smbd: dump SMB3+ session keys if debug parm is set

Use of previously added smb.conf global param.

Sample usage:

$ smbclient //localhost/scratch --option='debugencryption=yes' \
                                 -e -mSMB3 -U aaptel%aaptel -c quit
debug encryption: dumping generated session keys
Session Id    [0000] 26 48 BF FD 00 00 00 00                             &H......
Session Key   [0000] 63 D6 CA BC 08 C8 4A D2   45 F6 AE 35 AB 4A B3 3B   c.....J. E..5.J.;
Signing Key   [0000] 4E FE 35 92 AC 13 14 FC   C9 17 62 B1 82 20 A4 12   N.5..... ..b.. ..
App Key       [0000] A5 0F F4 8B 2F FB 0D FF   F2 BF EE 39 E6 6D F5 0A   ..../... ...9.m..
ServerIn Key  [0000] 2A 02 7E E1 D3 58 D8 12   4C 63 76 AE 59 17 5A E4   *.~..X.. Lcv.Y.Z.
ServerOut Key [0000] 59 F2 5B 7F 66 8F 31 A0   A5 E4 A8 D8 2F BA 00 38   Y.[.f.1. ..../..8

We can now simply pass -ouat:smb2_seskey_list:<sesid>,<seskey> to
wireshark or tshark:

$ tshark -ouat:smb2_seskey_list:2648BFFD00000000,63D6CABC08C84AD245F6AE35AB4AB33B \
          -Y smb2 -r capture.pcap -Tfields -e _ws.col.Info
Negotiate Protocol Response
Negotiate Protocol Request
Negotiate Protocol Response
Session Setup Request, NTLMSSP_NEGOTIATE
Session Setup Response, Error: STATUS_MORE_PROCESSING_REQUIRED, NTLMSSP_CHALLENGE
Session Setup Request, NTLMSSP_AUTH, User: WORKGROUP\aaptel
Session Setup Response
Tree Connect Request Tree: \\localhost\IPC$
Tree Connect Response
Decrypted SMB3;Ioctl Request FSCTL_DFS_GET_REFERRALS, File: \localhost\scratch
Decrypted SMB3;Ioctl Response, Error: STATUS_NOT_FOUND
Decrypted SMB3;Tree Disconnect Request
Decrypted SMB3;Tree Disconnect Response
Decrypted SMB3;Tree Connect Request Tree: \\localhost\scratch
Decrypted SMB3;Tree Connect Response
Decrypted SMB3;Tree Disconnect Request
Decrypted SMB3;Tree Disconnect Response

For more info on Wireshark decryption support see
https://wiki.samba.org/index.php/Wireshark_Decryption

Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Reviewed-by: Noel Power <npower@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Reviewed-by: David Disseldorp <ddiss@samba.org>
Autobuild-User(master): David Disseldorp <ddiss@samba.org>
Autobuild-Date(master): Sat Feb  9 21:43:25 CET 2019 on sn-devel-144