We add command line options for the user to change the start, stop, speed,
ifdown, and stampfile settings at runtime. This closes a Debian wishlist
bug [1].
Note that, in order to have the command line options overwrite the
defaults set in the configuration file, we split the command line parsing
code into a new function (parse_cmdline()). We then merged main() and
wmppp_routine().
We document the new options in the help text and in the man page. We also
take the opportunity to reformat the help text for the -i option and add
the -geometry option to the man page.
[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=293839
We actually include <sys/socket.h> instead of <bits/socket_type.h>, as it
returns an error: "Never include <bits/socket_type.h> directly; use
<sys/socket.h> instead."
Fixes "warning: null argument where non-null required" compiler warnings by
not passing NULL to strdup and "(warning) Conversion of string literal to
bool always evaluates to true" found by cppcheck.
