selftests: nettest: Fix typo in log and error messages for clarity

This patch corrects several logging and error message in nettest.c:
- Corrects function name in log messages "setsockopt" -> "getsockopt".
- Closes missing parentheses in "setsockopt(IPV6_FREEBIND)".
- Replaces misleading error text ("Invalid port") with the correct
  description ("Invalid prefix length").
- remove Redundant wording like "status from status" and clarifies
  context in IPC error messages.

These changes improve readability and aid in debugging test output.

Signed-off-by: Alok Tiwari <alok.a.tiwari@oracle.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250615084822.1344759-1-alok.a.tiwari@oracle.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>