nginx: Update SSL settings to current guidelines

This reduces the session cache size and adds the DHE-RSA-CHACHA20-POLY1305 cipher.

They're also recommending using audited DHE parameters (https://ssl-config.mozilla.org/ffdhe2048.txt, from RFC 7919) instead of generating random parameters, as random parameters might be less secure.

approved this merge request

resolved all threads

added 4 commits

• 5848a3c0...3d36b3b8 - 3 commits from branch master
• 98418998 - nginx: Update SSL settings to current guidelines

Compare with previous version

resolved all threads

mentioned in issue #602

mentioned in commit 6172c319

merged