test and comments for netshutdown

[qianxichen233]

Description

This PR adds some tests and comments for netshutdown_syscall. Current implementation of shutdown has several big issues, so only some basic tests could be done on shutdown right now.

Fixes # (issue)

1. add fd range check at the beginning of the shutdown
2. fixed a minor issue in setting connection state under _cleanup_socket_inner_helper

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• Test A - ut_lind_net_shutdown_bad_input
• Test B - ut_lind_net_shutdown_unix
• Test C - ut_lind_net_shutdown_inet

Checklist:

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• Any dependent changes have been added to a pull request and/or merged in other modules (native-client, lind-glibc, lind-project)

[davidge20]

lgtm !

[rupeshkoushik07]

LGTM!

[rennergade]

approved!