fix(s2): Harden S2_init_ctx using safe memset

This is a simple change to check the static analysis.

SonarQube is reporting:

This "memset" is likely to be optimized away by the compiler; either remove it or replace it with "memset_s".

While memset_s is suggested it is not implemented widely (it is optional),
at this stage i am following GNU standards until it stabilizes.

One other possible change it to harden compilation flags with:

  -fno-builtin-memset

Origin: #137
Relate-to: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1967.htm
Relate-to: https://en.cppreference.com/w/c/string/byte/memset
Relate-to: https://sourceware.org/glibc/manual/2.41/html_node/Erasing-Sensitive-Data.html
Relate-to: #100
Relate-to: SiliconLabsSoftware/z-wave-engine-application-layer#42
Relate-to: https://sourceware.org/bugzilla/show_bug.cgi?id=17879#c2
Signed-off-by: Philippe Coval <philippe.coval@silabs.com>

Author: rzr

applications/zpc/components/zwave/zwave_transports/s2/libs/zw-libs2/protocol/S2.c

@@ -1279,7 +1279,7 @@ S2_init_ctx(uint32_t home)
     return 0;
   }
 #endif
-  memset(ctx, 0, sizeof(struct S2));
+  explicit_bzero(ctx, sizeof(struct S2));
 
   ctx->my_home_id = home;
   ctx->loaded_keys = 0;
@@ -1329,7 +1329,7 @@ void
 S2_destroy(struct S2* p_context)
 {
   CTX_DEF
-  memset(ctxt, 0, sizeof(struct S2));
+  explicit_bzero(ctxt, sizeof(struct S2));
 #ifndef SINGLE_CONTEXT
   free(ctxt);
 #endif
@@ -2054,4 +2054,4 @@ static void S2_send_nls_node_list_report(struct S2* p_context, s2_connection_t*
   S2_send_data(ctxt, con, buf, SECURITY_2_V2_NLS_NODE_LIST_REPORT_LENGTH);
 }
 
-#endif
+#endif