esp32/lteppp: Don't send CR each time when invoking "lteppp_send_at_cmd"

@larox11 found this an when trying to send AT+CSIM commands 
longer than 500 bytes to the modem. As the buffer behind this
method is only 127 bytes long and the strcmp was evaluated
erroneous, this stopped users sending longer commands in several
chunks.

Author: amotl

esp32/lte/lteppp.c

@@ -658,7 +658,7 @@ static bool lteppp_send_at_cmd_exp (const char *cmd, uint32_t timeout, const cha
         // uart_read_bytes(LTE_UART_ID, (uint8_t *)tmp_buf, sizeof(tmp_buf), 5 / portTICK_RATE_MS);
         // then send the command
         uart_write_bytes(LTE_UART_ID, cmd, cmd_len);
-        if (strcmp(cmd, "+++")) {
+        if (!strcmp(cmd, "+++")) {
             uart_write_bytes(LTE_UART_ID, "\r", 1);
         }
         uart_wait_tx_done(LTE_UART_ID, LTE_TRX_WAIT_MS(cmd_len) / portTICK_RATE_MS);