vmctl: start: Require one interface at minimium with -i

[Klemens Nanni]

It makes no sense to allow zero interfaces;  either a positive count is
given or -i is omitted entirely.  vm.conf(5) does not allow interface
configuration that results in zero interfaces either.

        $ doas vmctl start -Li0 -b ~/bsd.rd foo      
        vmctl: starting without disks
        vmctl: started vm 6 successfully, tty /dev/ttyph

Diff below raises the minimum to one and tells more about invalid counts
with the usual strtonum(3) idiom:

        $ doas vmctl start -Li-1 -b ~/bsd.rd foo
        vmctl: invalid count "-1": too small
        vmctl: invalid interface count: -1
        $ doas ./obj/vmctl start -Li0 -b ~/bsd.rd foo 
        vmctl: count is too small: 0
        vmctl: invalid interface count: 0

Those duplicate errors aren't easily merged without breaking consistency
with how all the command line flags are passed, so I did nothing about
this.

OK?


Index: main.c
===================================================================
RCS file: /cvs/src/usr.sbin/vmctl/main.c,v
retrieving revision 1.58
diff -u -p -r1.58 main.c
--- main.c      23 Aug 2019 07:55:20 -0000      1.58
+++ main.c      25 Oct 2019 22:48:49 -0000
@@ -373,9 +373,9 @@ parse_ifs(struct parse_result *res, char
        const char      *error;
 
        if (word != NULL) {
-               val = strtonum(word, 0, INT_MAX, &error);
+               val = strtonum(word, 1, INT_MAX, &error);
                if (error != NULL)  {
-                       warnx("invalid count \"%s\": %s", word, error);
+                       warnx("count is %s: %s", error, word);
                        return (-1);
                }
        }