Actually set the FREQ_FIXED flag
Actually set the FREQ_FIXED flag

This is a flag, so it has a payload of NULL in the netlink `nla_put_flag` command. We previously were not setting this flag, which resulted in off-channel scans despite us setting a fixed frequency.
roolebo/pyroute2,roolebo/pyroute2,simudream/pyroute2,little-dude/pyroute2,mtiny/pyroute2,tomislacker/python-iproute2,little-dude/pyroute2,mtiny/pyroute2,drzaeus77/pyroute2,vodik/pyroute2,tomislacker/python-iproute2,vodik/pyroute2,drzaeus77/pyroute2,little-dude/pyroute2,simudream/pyroute2