wlantest: Verify Beacon frame MME even after Probe Response reception

wlantest: Verify Beacon frame MME even after Probe Response reception

rx_mgmt_beacon() was skipping all steps after a Probe Response frame
from the AP had been processed. This is expected for the parts that were
updating the bss entry information, but the checks for beacon protection
should not be skipped in this manner.

Skip onlu the updating parts while checking that beacon protection is
used correctly to make this more useful.

Signed-off-by: Jouni Malinen <quic_jouni@quicinc.com>