fix: invalid indirect read from stack

The following verifier log is caused by uninitilized stack variable.

```log
couldn't init manager xxx verifier error:load program: permission denied:
	0: R1=ctx(off=0,imm=0) R10=fp0
	; struct sock *sk = (struct sock *)PT_REGS_PARM1(ctx);
	0: (79) r2 = *(u64 *)(r1 +112)        ; R1=ctx(off=0,imm=0) R2_w=scalar()
	1: (b7) r3 = 1                        ; R3_w=1
	; conn.is_destroy = 1;
	2: (73) *(u8 *)(r10 -8) = r3          ; R3_w=1 R10=fp0 fp-8=1
	; conn.sock = (u64)sk;
	3: (7b) *(u64 *)(r10 -16) = r2        ; R2_w=scalar() R10=fp0 fp-16_w=mmmmmmmm
	4: (bf) r4 = r10                      ; R4_w=fp0 R10=fp0
	;
	5: (07) r4 += -64                     ; R4_w=fp-64
	; bpf_perf_event_output(ctx, &connect_events, BPF_F_CURRENT_CPU, &conn,
	6: (18) r2 = 0xffff8dd41e9c0000       ; R2_w=map_ptr(off=0,ks=4,vs=4,imm=0)
	8: (18) r3 = 0xffffffff               ; R3_w=4294967295
	10: (b7) r5 = 64                      ; R5_w=64
	11: (85) call bpf_perf_event_output#25
	invalid indirect read from stack R4 off -64+0 size 64
	processed 10 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
```

Signed-off-by: Leon Hwang <hffilwlqm@gmail.com>

kern/openssl.h

@@ -633,8 +633,9 @@ int retprobe_accept4(struct pt_regs* ctx) {
 SEC("kprobe/tcp_v4_destroy_sock")
 int probe_tcp_v4_destroy_sock(struct pt_regs* ctx) {
     struct sock *sk = (struct sock *)PT_REGS_PARM1(ctx);
-
     struct connect_event_t conn;
+
+    __builtin_memset(&conn, 0, sizeof(conn));
     conn.sock = (u64)sk;
     conn.is_destroy = 1;