Revert "n-dhcp4: work around compiler warning in n_dhcp4_socket_packet_send()"

We have now a different solution using c_errno() in packet_sendto_udp().

This reverts commit 4686e9baef.

shared/n-dhcp4/src/n-dhcp4-socket.c

@@ -348,8 +348,7 @@ static int n_dhcp4_socket_packet_send(int sockfd,
                 .sll_halen = halen,
         };
         const void *buf;
-        size_t n_buf;
-        size_t len = 0;
+        size_t n_buf, len;
         int r;
 
         c_assert(halen <= sizeof(haddr.sll_addr));