cl_netfps: reduce pings by synchronising when possible, related fixes

cl_netfps: reduce pings by synchronising when possible, related fixes

Fixes possibility of input frequency to exceed cl_netfps in certain
configurations.

Fixes possibility of rate limiting to reduce input frequency more than
it should.

Fixes timescale affecting input frequency (now consistent with client
FPS and server HZ being unaffected by timescale).

History of this code (most recent first):
1b6ea396b616e359cfe98d1e85e8e7a9ac571e91
528b92ffab3a9ab09770310e2796adbe5f0f1e20
79e332ad14e7ec9dbd2702a2d28127f7600f0678
663279ba8feeb4c114df0950bbc820f3bb32dcdc
21beb5fe4fa2e1f1b7591a4a1f6013b82186912f

Signed-off-by: bones_was_here <bones_was_here@xonotic.au>