WMM-AC: Fix hostapd processing of ADDTS Request and add test code

WMM-AC: Fix hostapd processing of ADDTS Request and add test code

Calculate the estimated medium time using integer variables since there
is no real need to use floating point arithmetics here. In addition,
make sure there is no division by zero regardless of how invalid the
request from the station is. Reject invalid parameters and refuse
requests that would take most of the bandwidth by themselves.

Add test code into wpa_supplicant mlme.c to allow WMM-AC negotiation to
be tested with driver_test.