man wpa_supplicant: Clearly state which options are given per interface

man wpa_supplicant: Clearly state which options are given per interface

Documentation appeared a little vague about which options are global and
which are tied to a particular interface. This leads to confusion when
using certain combinations of options, e.g. the command "wpa_supplicant
-c /etc/wpa_supplican.conf -u" will not do what is intuitively expected
from it - it will not read the config file given with -c option because
no -i option was given. This command is still valid because -u option is
used. The wpa_supplicant running like this will also not listen on any
control socket, because the socket file name is usually given in the
config file. This command line also happens to be the default in Fedora 9.
This patch does not try to change any behaviour, but rather document
these nuances clearly.