dhcp-server: don't assign sendmsg() return value to "int"

The type is "ssize_t", not "int", let's be accurate about that, as these
types are different on some archs.

Given that we don't actually care about the return value reall, drop
the whole assignment, just check if negative.

src/libsystemd-network/sd-dhcp-server.c

@@ -313,7 +313,6 @@ static int dhcp_server_send_udp(sd_dhcp_server *server, be32_t destination,
         };
         struct cmsghdr *cmsg;
         struct in_pktinfo *pktinfo;
-        int r;
 
         assert(server);
         assert(server->fd >= 0);
@@ -337,8 +336,7 @@ static int dhcp_server_send_udp(sd_dhcp_server *server, be32_t destination,
         pktinfo->ipi_ifindex = server->ifindex;
         pktinfo->ipi_spec_dst.s_addr = server->address;
 
-        r = sendmsg(server->fd, &msg, 0);
-        if (r < 0)
+        if (sendmsg(server->fd, &msg, 0) < 0)
                 return -errno;
 
         return 0;