client: Improve input packet timing (netfps)

client: Improve input packet timing (netfps)

Increase min netfps to 10 (matches min ticrate).

Skip packettime calculations for 0ms packets.

Cap netfps when ticrate stat is available:
soft limit 2x, hard limit < 4x server frame rate.

Set packettime to (largest multiple of realframetime) <= packettime.
Prevents packet rates lower than cl_netfps or server frame rate,
eg: cl_netfps 60 and cl_maxfps 250 would otherwise send only 50 netfps.

Allow for float error when deciding if it's time to send yet.

Accumulate realframetime instead of storing host.realtime.
Fixes low packet rates in some configurations,
eg: with cl_maxfps 125 and cl_netfps 125 it would not send every frame,
as host.realtime - lastpackettime was often well below (or above) 8ms.

Authored by bones_was_here
https://gitlab.com/xonotic/darkplaces/-/merge_requests/112

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@13113 d7cf8633-e32d-0410-b094-e92efae38249