net: core: Add a GID field to struct sock.

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8KU3B


CVE: NA

--------------------------------

UID and GID are requested as filters for socketmap, but we can only get
UID from sock structure. This patch adds GID field to struct sock as UID.

Signed-off-by: Lu Wei <luwei32@huawei.com>
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>