lib-dropbear: do not call disallow_core

Presumably for safety purposes, dropbear sets the maximum size of a core
dump for its process to zero, thus disabling it.
My guess is that it's done to avoid leaks of any sort.

Unikraft, however, does not seem to implement the concept of core dumps.
Attempting to set this limit will result in a non-harmless message
saying "Unsupported resource". It doesn't break anything but I thought
that it would be nice to get rid of this confusing message.

Resource limits that are supported in Unikraft can be seen here:
https://github.com/unikraft/unikraft/blob/254bfe2748749336d077ba43153d8751d6faf1d9/lib/posix-process/deprecated.c#L327

lib/lib-dropbear/patches/0001-Do-not-call-disallow_core.patch

@@ -0,0 +1,25 @@
+From 6018a0c5e28d774a70d74526c2015234d31ebb7e Mon Sep 17 00:00:00 2001
+From: Adam Olech <me@aole.ch>
+Date: Wed, 29 Nov 2023 01:02:07 +0100
+Subject: [PATCH] Do not call disallow_core
+
+---
+ svr-main.c | 2 --
+ 1 file changed, 2 deletions(-)
+
+diff --git a/svr-main.c b/svr-main.c
+index 9234361..dd939d1 100644
+--- a/svr-main.c
++++ b/svr-main.c
+@@ -53,8 +53,6 @@ int main(int argc, char ** argv)
+ 	_dropbear_exit = svr_dropbear_exit;
+ 	_dropbear_log = svr_dropbear_log;
+
+-	disallow_core();
+-
+ 	if (argc < 1) {
+ 		dropbear_exit("Bad argc");
+ 	}
+-- 
+2.43.0
+