examples/rust-gcoap: Update stack size

Tests with a particle-xenon show 5KiB free stack now; before, that would
have been an overflow by 3KiB.

examples/rust-gcoap/Makefile

@@ -9,7 +9,7 @@ RIOTBASE ?= $(CURDIR)/../..
 
 # Basic networking, and gcoap
 USEMODULE += gcoap
-USEMODULE += netdev_default
+#USEMODULE += netdev_default
 USEMODULE += auto_init_gnrc_netif
 USEMODULE += gnrc_ipv6_default
 USEMODULE += gnrc_icmpv6_echo
@@ -23,6 +23,10 @@ USEMODULE += ztimer_sec
 USEMODULE += vfs
 USEMODULE += constfs
 
+USEMODULE += vfs_default
+USEMODULE += littlefs2
+USEMODULE += vfs_auto_format
+
 # for the "saul" feature of riot-coap-handler-demos
 USEMODULE += saul_default
 
@@ -34,10 +38,9 @@ DEVELHELP ?= 1
 # Change this to 0 show compiler invocation lines by default:
 QUIET ?= 1
 
-# Add 8k extra stack: The Rust examples take more of it than gcoap expects,
-# presumably because the example use the standard library's sting formatting
-# instead of one of the more optimized formatters.
-CFLAGS += -DGCOAP_STACK_SIZE='(THREAD_STACKSIZE_DEFAULT+DEBUG_EXTRA_STACKSIZE+sizeof(coap_pkt_t)+8192)'
+# Add 16k extra stack: The Rust examples take more of it than gcoap expects,
+# for reasons that are not fully understood (it's not the string formatter).
+CFLAGS += -DGCOAP_STACK_SIZE='(THREAD_STACKSIZE_DEFAULT+DEBUG_EXTRA_STACKSIZE+sizeof(coap_pkt_t)+16384)'
 # This thread needs some more stack for printing the addresses, once more being
 # hit by string formatting.
 CFLAGS += -DTHREAD_STACKSIZE_MAIN='(THREAD_STACKSIZE_DEFAULT+THREAD_EXTRA_STACKSIZE_PRINTF+2048)'