selftests/net: add tcp_port_share to .gitignore

Add the tcp_port_share test binary to .gitignore to avoid
accidentally staging the build artifact.

Signed-off-by: Gopi Krishna Menon <krishnagopi487@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250929163140.122383-1-krishnagopi487@gmail.com


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