TLS: added Encrypt-Then-MAC extension

[strayge]

Checklist:

• If you are new to Scapy: I have checked CONTRIBUTING.md (esp. section submitting-pull-requests)
• I squashed commits belonging together
• I added unit tests or explained why they are not relevant
• I executed the regression tests for Python2 and Python3 (using tox or, cd test && ./run_tests_py2, cd test && ./run_tests_py3)
• If the PR is still not finished, please create a Draft Pull Request

Description

Added support Encrypt-then-MAC extension for TLS protocol (RFC 7366).

Required and contains #2797 because openssl don't have command line options to disable Extended-Master-Secred, so test suite contains example with both extensions setted.

• fixed second part of TLS does not support Encrypt-then-MAC \ Extended Master Secret extensions #2784 (first part fixed by #2403 improvement: EXT MS TLS 1.2 #2797)

Implementation only for block ciphers

Encrypt-Then-Mac not supported by AEAD ciphers (according to RFC).

For TLS_PSK_WITH_CHACHA20_POLY1305_SHA256 (0xccab) and TLS_RSA_WITH_RC4_128_SHA (0x0005) openssl 1.1.1g does not support Encrypt-Then-Mac (presents in ClientHello, but missed in ServerHello response).

Same behaviour for GnuTLS 3.6.13 with TLS_RSA_WITH_RC4_128_SHA (0x0005) and TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256 (0xcca8).

So it is looks like currently Encrypt-Then-Mac implemented only for block ciphers.

[codecov]

Codecov Report

Merging #2811 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2811      +/-   ##
==========================================
+ Coverage   88.13%   88.15%   +0.01%     
==========================================
  Files         254      254              
  Lines       54189    54196       +7     
==========================================
+ Hits        47762    47776      +14     
+ Misses       6427     6420       -7     

Impacted Files	Coverage Δ
scapy/layers/tls/handshake.py	83.84% <100.00%> (+0.01%)	⬆️
scapy/layers/tls/record.py	90.78% <100.00%> (+0.95%)	⬆️
scapy/layers/tls/session.py	83.78% <100.00%> (-0.65%)	⬇️
scapy/arch/bpf/core.py	86.82% <0.00%> (-0.78%)	⬇️
scapy/arch/windows/__init__.py	68.50% <0.00%> (-0.19%)	⬇️
scapy/layers/inet.py	74.13% <0.00%> (+0.16%)	⬆️
scapy/arch/libpcap.py	82.03% <0.00%> (+1.69%)	⬆️
scapy/layers/tls/crypto/cipher_block.py	97.67% <0.00%> (+2.32%)	⬆️

[gpotter2]

Great PR ! Thanks a lot for this work.
I've rebased it against master, will merge it once the checks pass.