bpf: fix same insn cannot be used with different pointers in proxy.h

With the following helm config enabled, Cilium Agent fails to load BPF programs.

The error only occurs if verbose datapath logging is enabled.

```
debug:
  enabled: true
  verbose: "datapath"
bpf:
  tproxy: false
```

error:

```
; sk = sk_lookup_udp(ctx, tuple, len, BPF_F_CURRENT_NETNS, 0);
829: (bf) r1 = r6
830: (b4) w3 = 36
831: (b7) r4 = -1
832: (b7) r5 = 0
833: (85) call bpf_sk_lookup_udp#85
last_idx 833 first_idx 827
regs=8 stack=0 before 832: (b7) r5 = 0
regs=8 stack=0 before 831: (b7) r4 = -1
regs=8 stack=0 before 830: (b4) w3 = 36
834: (b4) w7 = -178
; if (!sk)
835: (15) if r0 == 0x0 goto pc+38
 R0_w=sock(id=0,ref_obj_id=29,off=0,imm=0) R6=ctx(id=0,off=0,imm=0) R7_w=inv4294967118 R8=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R9=inv(id=22,umax_value=65535,var_off=(0x0; 0xffff)) R10=fp0 fp-16=???mmmmm fp-24=mmmmmmmm fp-32=mmmmmmmm fp-40=mmmmmmmm fp-48=mmmmmmmm fp-72=????mmmm fp-80=mmmmmmmm fp-88=mmmmmmmm refs=29
;
836: (61) r1 = *(u32 *)(r6 +16)
837: (63) *(u32 *)(r10 -104) = r1
838: (61) r7 = *(u32 *)(r0 +4)
same insn cannot be used with different pointers
processed 1261 insns (limit 1000000) max_states_per_insn 4 total_states 68 peak_states 67 mark_read 19
```

This commit fixes this issue by extracting a variable `family`.

Signed-off-by: Marco Hofstetter <marco.hofstetter@isovalent.com>

bpf/lib/proxy.h

@@ -18,6 +18,7 @@ assign_socket_tcp(struct __ctx_buff *ctx,
 	int result = DROP_PROXY_LOOKUP_FAILED;
 	struct bpf_sock *sk;
 	__u32 dbg_ctx;
+	__u32 family;
 
 	sk = skc_lookup_tcp(ctx, tuple, len, BPF_F_CURRENT_NETNS, 0);
 	if (!sk)
@@ -28,7 +29,8 @@ assign_socket_tcp(struct __ctx_buff *ctx,
 	if (established && sk->state == BPF_TCP_LISTEN)
 		goto release;
 
-	dbg_ctx = sk->family << 16 | ctx->protocol;
+	family = sk->family;
+	dbg_ctx = family | ctx->protocol;
 	result = sk_assign(ctx, sk, 0);
 	cilium_dbg(ctx, DBG_SK_ASSIGN, -result, dbg_ctx);
 	if (result == 0)
@@ -49,12 +51,14 @@ assign_socket_udp(struct __ctx_buff *ctx,
 	int result = DROP_PROXY_LOOKUP_FAILED;
 	struct bpf_sock *sk;
 	__u32 dbg_ctx;
+	__u32 family;
 
 	sk = sk_lookup_udp(ctx, tuple, len, BPF_F_CURRENT_NETNS, 0);
 	if (!sk)
 		goto out;
 
-	dbg_ctx = sk->family << 16 | ctx->protocol;
+	family = sk->family;
+	dbg_ctx = family << 16 | ctx->protocol;
 	result = sk_assign(ctx, sk, 0);
 	cilium_dbg(ctx, DBG_SK_ASSIGN, -result, dbg_ctx);
 	if (result == 0)