esp8266: Set suitable values for axtls's RT_MAX_PLAIN_LENGTH & RT_EXTRA.

esp8266/Makefile

@@ -207,4 +207,4 @@ axtls:
 	cd ../lib/axtls; cp config/upyconfig config/.config
 	cd ../lib/axtls; make oldconfig -B
 	cd ../lib/axtls; make clean
-	cd ../lib/axtls; make all CC="$(CC)" LD="$(LD)" CFLAGS_EXTRA="$(CFLAGS_XTENSA) -Dabort=abort_"
+	cd ../lib/axtls; make all CC="$(CC)" LD="$(LD)" CFLAGS_EXTRA="$(CFLAGS_XTENSA) -Dabort=abort_ -DRT_MAX_PLAIN_LENGTH=1024 -DRT_EXTRA=3072"