libiwinfo: ignore log messages from wpa_supplicant while scanning

libiwinfo: ignore log messages from wpa_supplicant while scanning

wpa_supplicant may send log and event messages intermixed with the
expected scan results.  This makes "iwinfo wlan0 scan" and LuCI
"site survey" display nothing when many AP's are around.

Eliminate the CTRL-EVENT-BSS-ADDED events, interspersed log messages,
lines with unexpected format.  Increase timeout to handle the max
number of channels (2.4, 3.6, 4.9, 5 GHz).  Insure receive buffer is
null-terminated.

Signed-off-by: Jean-Pierre Tosoni <jp.tosoni@acksys.fr>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@36888 3c298f89-4303-0410-b956-a3cf2f4a3e73