The current channel flags printing is very strange and messy,
in LAR we sometimes print the channel number and sometimes the
frequency, in both we print a calculated value (whether ad-hoc
is supported or not) etc.

Unify all this to
 * print the channel number, not the frequency
 * remove the band print (2.4/5.2 GHz, it's obvious)
 * remove the calculated Ad-Hoc print

Doing all of this also gets the length of the string to a max
of 101 characters, which is below the max of 110 for tracing,
and thus avoids the warning that came up on certain channels
with certain flag combinations.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>