bpf: Allow error injection for update_socket_protocol

The "update_socket_protocol" interface is designed to empower user space
with the capability to customize and modify socket protocols leveraging
BPF methods. Currently, it has only granted the fmod_ret permission,
allowing for modifications to return values. We are extending the
permissions further by 'ALLOW_ERROR_INJECTION', thereby facilitating
the development of user-space programs with enhanced flexibility and
convenience.

When we attempt to modify the return value of "update_socket_protocol"
to "IPPROTO_MPTCP" using the below code based on the BCC tool:

'''
int kprobe__update_socket_protocol(void* ctx)
{
    ...
    bpf_override_return(ctx,IPPROTO_MPTCP);
    ...
}
'''

But an error occurs:

'''
ioctl(PERF_EVENT_IOC_SET_BPF): Invalid argument
Traceback (most recent call last):
  File "/media/yangang/work/Code/BCC/test.py", line 27, in <module>
    b = BPF(text=prog)
        ^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/bcc/__init__.py", line 487, \
                  in __init__ self._trace_autoload()
  File "/usr/lib/python3/dist-packages/bcc/__init__.py", line 1466, \
                  in _trace_autoload self.attach_kprobe(
  File "/usr/lib/python3/dist-packages/bcc/__init__.py", line 855,\
                  in attach_kprobe
    raise Exception("Failed to attach BPF program %s to kprobe %s"
Exception: Failed to attach BPF program b'kprobe__update_socket_protocol' \
  to kprobe b'update_socket_protocol', it's not traceable \
  (either non-existing, inlined, or marked as "notrace")
'''

This patch can fix the issue.

Suggested-by: Geliang Tang <[email protected]>
Signed-off-by: Gang Yan <[email protected]>

Author: Gang Yan

net/socket.c

@@ -1695,6 +1695,7 @@ __weak noinline int update_socket_protocol(int family, int type, int protocol)
 {
 	return protocol;
 }
+ALLOW_ERROR_INJECTION(update_socket_protocol, ERRNO);
 
 __bpf_hook_end();