Replace usages of l_settings_get_value with l_settings_get_string, which
will make sure the returned strings are unescaped but also allocates
memeory and forces us to use l_free on most of the strings. Some of
these strings we explicitly set with l_settings_set_string() in our code
so when we retrieved them with l_settings_get_value() we would receive a
different string if there were any escapable characters in the string.
I didn't replace any of the l_settings_get_value() uses where we're just
checking whether a setting is present, or those which are hexstrings or
EAP method names assuming that they can't have any special characters,
although this isn't future proof. I did use l_settings_get_string() for
file paths though.
Accept two setting IDs in eap_append_secret, first for the username and
second for the password in case of the EAP_SECRET_REMOTE_USER_PASSWORD
EAP secret type. In all other cases only the first setting is used.
Until now for EAP_SECRET_REMOTE_USER_PASSWORD secrets we'd generate the
two setting names by adding different suffixes to the ID parameter.
Using the two different setting names automatically fixes the issues
with using the EAP Identity returned by the agent in EAP-MSCHAPv2 and
EAP-PWD.
