tests: Fix missing function on some rrm test case error paths

Import vht_supported from test_ap_vht to fix the following issue:

rrm_beacon_req_table_vht run failed: global name 'vht_supported' is not defined

Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>

tests/hwsim/test_rrm.py

@@ -19,6 +19,7 @@ from wpasupplicant import WpaSupplicant
 from utils import HwsimSkip, alloc_fail, fail_test, wait_fail_trigger
 from test_ap_ht import clear_scan_cache
 from remotehost import remote_compatible
+from test_ap_vht import vht_supported
 
 def check_rrm_support(dev):
     rrm = int(dev.get_driver_status_field("capa.rrm_flags"), 16)