Make tests work on public repo as well

PUBLISHED_FROM=78acb18d597b6f47f31da13087fa6685f21ce445

src/common/platforms/esp/slip.c

@@ -0,0 +1,35 @@
+#include "rom_functions.h"
+
+void SLIP_send(uint8_t *pkt, uint32_t size) {
+  send_packet(pkt, size);
+}
+
+uint32_t SLIP_recv(void *pkt, uint32_t max_len) {
+  uint8_t c;
+  uint32_t len = 0;
+  uint8_t *p = (uint8_t *) pkt;
+  do {
+    c = uart_rx_one_char_block();
+  } while (c != '\xc0');
+  while (len < max_len) {
+    c = uart_rx_one_char_block();
+    if (c == '\xc0') return len;
+    if (c == '\xdb') {
+      c = uart_rx_one_char_block();
+      if (c == '\xdc') {
+        c = '\xc0';
+      } else if (c == '\xdd') {
+        c = '\xdb';
+      } else {
+        len = 0;
+        break; /* Bad esc sequence. */
+      }
+    }
+    *p++ = c;
+    len++;
+  }
+  do {
+    c = uart_rx_one_char_block();
+  } while (c != '\xc0');
+  return len;
+}