wpa_supplicant: Parse int values in different bases and reject invalid

wpa_supplicant: Parse int values in different bases and reject invalid

Instead of using atoi(), use strtol() which allows checking if
the configuration values are valid integers and can understand
more than just decimal (also hexadecimal and octal). This not
only allows specifying some fields in hex (which can be useful)
but also rejecting invalid configurations, e.g.,
        disassoc_low_ack=27 * 2
which was previously read as just 27.

Signed-hostap: Johannes Berg <johannes.berg@intel.com>