BUILD: ssl: buggy -Werror=dangling-pointer since gcc 13.0

GCC complains about swapping 2 heads list, one local and one global.

    gcc -Iinclude  -O2 -g -Wall -Wextra -Wundef -Wdeclaration-after-statement -Wfatal-errors -Wtype-limits -Wshift-negative-value -Wshift-overflow=2 -Wduplicated-cond -Wnull-dereference -fwrapv -Wno-address-of-packed-member -Wno-unused-label -Wno-sign-compare -Wno-unused-parameter -Wno-clobbered -Wno-missing-field-initializers -Wno-cast-function-type -Wno-string-plus-int -Wno-atomic-alignment -Werror     -DDEBUG_STRICT -DDEBUG_MEMORY_POOLS -DUSE_EPOLL  -DUSE_NETFILTER -DUSE_POLL -DUSE_THREAD  -DUSE_BACKTRACE -DUSE_TPROXY -DUSE_LINUX_TPROXY -DUSE_LINUX_SPLICE -DUSE_LIBCRYPT -DUSE_CRYPT_H  -DUSE_GETADDRINFO -DUSE_OPENSSL  -DUSE_SSL -DUSE_LUA -DUSE_ACCEPT4  -DUSE_ZLIB  -DUSE_CPU_AFFINITY -DUSE_TFO -DUSE_NS -DUSE_DL -DUSE_RT  -DUSE_MATH    -DUSE_SYSTEMD  -DUSE_PRCTL  -DUSE_THREAD_DUMP   -DUSE_QUIC   -DUSE_SHM_OPEN   -DUSE_PCRE -DUSE_PCRE_JIT   -I/github/home/opt/include -I/usr/include  -DCONFIG_HAPROXY_VERSION=\"2.8-dev8-7d23e8d1a6db\" -DCONFIG_HAPROXY_DATE=\"2023/04/24\" -c -o src/ssl_sample.o src/ssl_sample.c
    In file included from include/haproxy/pool.h:29,
                     from include/haproxy/chunk.h:31,
                     from include/haproxy/dynbuf.h:33,
                     from include/haproxy/channel.h:27,
                     from include/haproxy/applet.h:29,
                     from src/ssl_sock.c:47:
    src/ssl_sock.c: In function 'tlskeys_finalize_config':
    include/haproxy/list.h:48:88: error: storing the address of local variable 'tkr' in 'tlskeys_reference.p' [-Werror=dangling-pointer=]
       48 | #define LIST_INSERT(lh, el) ({ (el)->n = (lh)->n; (el)->n->p = (lh)->n = (el); (el)->p = (lh); (el); })
          |                                                                                ~~~~~~~~^~~~~~
    src/ssl_sock.c:1086:9: note: in expansion of macro 'LIST_INSERT'
     1086 |         LIST_INSERT(&tkr, &tlskeys_reference);
          |         ^~~~~~~~~~~
    compilation terminated due to -Wfatal-errors.

This appears with gcc 13.0.

The fix uses LIST_SPLICE() instead of inserting the head of the local
list in the global list.

Should fix issue #2136 .

src/ssl_sock.c

@@ -1083,8 +1083,7 @@ static int tlskeys_finalize_config(void)
 	}
 
 	/* swap root */
-	LIST_INSERT(&tkr, &tlskeys_reference);
-	LIST_DELETE(&tkr);
+	LIST_SPLICE(&tlskeys_reference, &tkr);
 	return ERR_NONE;
 }
 #endif /* SSL_CTRL_SET_TLSEXT_TICKET_KEY_CB */