[Fix] Enforce server-controlled HTTP map refresh intervals

[Fix] Enforce server-controlled HTTP map refresh intervals

Prevent aggressive HTTP map polling by implementing proper interval bounds:
- Cap absurdly high Expires headers (>8h) to min(map_interval * 10, 8h)
- Enforce configured map_interval as minimum when server requests faster refresh
- Apply 10 minute minimum interval when no Expires header and low map_interval
- Simplify logic by consolidating interval calculation in single function

This change ensures servers can control refresh rates and prevents clients
from causing issues with overly aggressive polling behavior.