[Pal/Linux] Fix vDSO range retrieval

This change causes PAL to report the vDSO range based on
`/proc/self/maps`, instead of parsing the ELF mapped there and
processing PT_LOAD commands.

On my system, the former method returns 1 page, even though according to
`/proc/self/maps` vDSO occupies 2 pages. As a result, under some
circumstances (Docker and ASLR disabled) LibOS tries to map memory over
vDSO.

Signed-off-by: Paweł Marczewski <pawel@invisiblethingslab.com>

Pal/src/host/Linux/db_main.c

@@ -237,8 +237,8 @@ noreturn void pal_linux_main(void* initial_rsp, void* fini_callback) {
         INIT_FAIL(-ret, "getting vdso and vvar ranges failed");
     }
 
-    if (!g_vdso_start && !g_vdso_end) {
-        /* We did not get vdso address from the auxiliary vector. */
+    if (vdso_start || vdso_end) {
+        /* Override the range retrieved by parsing vdso: the actual mapped range might be bigger. */
         g_vdso_start = vdso_start;
         g_vdso_end = vdso_end;
     }