esp32: fix random pkt cause esp32 watchdog

This change fixes the ESP32 watchdog issue. When the MPDU of AMPDU is longer than 1600B,
esp32 will check whether the last 4B is DEADBEEF, if it's not DEADBEEF, it will assert
and the assert will cause esp32 watchdog. The solution is to init the last 4B to DEADBEEF
when malloc new ebuf for the packet longer than 1600B.

diff --git a/components/esp32/lib b/components/esp32/lib
index ea9c156e8a67d27623eab6f98ce5a55a00c8fb19..e2e5781dc27e638c5e63f85bc23590dd21af1619 160000 (submodule)
--- a/components/esp32/lib
+++ b/components/esp32/lib
@@ -1 +1 @@
-Subproject commit ea9c156e8a67d27623eab6f98ce5a55a00c8fb19
+Subproject commit e2e5781dc27e638c5e63f85bc23590dd21af1619