bpf: NULL pointer check is not needed in BPF_CGROUP_RUN_PROG_INET_SOCK

sk is already allocated in inet_create/inet6_create, hence when
BPF_CGROUP_RUN_PROG_INET_SOCK is executed sk will never be NULL.

The logic is as bellow,
	sk = sk_alloc();
	if (!sk)
		goto out;
	BPF_CGROUP_RUN_PROG_INET_SOCK(sk);

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

include/linux/bpf-cgroup.h

@@ -96,7 +96,7 @@ int __cgroup_bpf_check_dev_permission(short dev_type, u32 major, u32 minor,
 #define BPF_CGROUP_RUN_PROG_INET_SOCK(sk)				       \
 ({									       \
 	int __ret = 0;							       \
-	if (cgroup_bpf_enabled && sk) {					       \
+	if (cgroup_bpf_enabled) {					       \
 		__ret = __cgroup_bpf_run_filter_sk(sk,			       \
 						 BPF_CGROUP_INET_SOCK_CREATE); \
 	}								       \