resolved: be more careful with types in dns_stream_writev()

Let's not name a variable of type ssize_t "r". We usually use "r" for
return values of API calls that return some kind of error as in int.
This creates a lot of confusion if used differently here, which actually
resulted in connect()'s return value being assigned to this mistyped "r"
by accident.

Let's rename the variable "m" hence, and not use it for connect() return
values.

src/resolve/resolved-dns-stream.c

@@ -193,7 +193,7 @@ static int dns_stream_identify(DnsStream *s) {
 }
 
 ssize_t dns_stream_writev(DnsStream *s, const struct iovec *iov, size_t iovcnt, int flags) {
-        ssize_t r;
+        ssize_t m;
 
         assert(s);
         assert(iov);
@@ -203,13 +203,13 @@ ssize_t dns_stream_writev(DnsStream *s, const struct iovec *iov, size_t iovcnt,
                 ssize_t ss;
                 size_t i;
 
-                r = 0;
+                m = 0;
                 for (i = 0; i < iovcnt; i++) {
                         ss = dnstls_stream_write(s, iov[i].iov_base, iov[i].iov_len);
                         if (ss < 0)
                                 return ss;
 
-                        r += ss;
+                        m += ss;
                         if (ss != (ssize_t) iov[i].iov_len)
                                 continue;
                 }
@@ -223,28 +223,28 @@ ssize_t dns_stream_writev(DnsStream *s, const struct iovec *iov, size_t iovcnt,
                         .msg_namelen = s->tfo_salen
                 };
 
-                r = sendmsg(s->fd, &hdr, MSG_FASTOPEN);
-                if (r < 0) {
+                m = sendmsg(s->fd, &hdr, MSG_FASTOPEN);
+                if (m < 0) {
                         if (errno == EOPNOTSUPP) {
                                 s->tfo_salen = 0;
-                                r = connect(s->fd, &s->tfo_address.sa, s->tfo_salen);
-                                if (r < 0)
+                                if (connect(s->fd, &s->tfo_address.sa, s->tfo_salen) < 0)
                                         return -errno;
 
-                                r = -EAGAIN;
-                        } else if (errno == EINPROGRESS)
-                                r = -EAGAIN;
-                        else
-                                r = -errno;
+                                return -EAGAIN;
+                        }
+                        if (errno == EINPROGRESS)
+                                return -EAGAIN;
+
+                        return -errno;
                 } else
                         s->tfo_salen = 0; /* connection is made */
         } else {
-                r = writev(s->fd, iov, iovcnt);
-                if (r < 0)
-                        r = -errno;
+                m = writev(s->fd, iov, iovcnt);
+                if (m < 0)
+                        return -errno;
         }
 
-        return r;
+        return m;
 }
 
 static ssize_t dns_stream_read(DnsStream *s, void *buf, size_t count) {