git_connect(): refactor the port handling for ssh

git_connect(): refactor the port handling for ssh

Use get_host_and_port() even for ssh.
Remove the variable port git_connect(), and simplify parse_connect_url()
Use only one return point in git_connect(), doing the free() and return conn.

t5601 had 2 corner test cases which now pass.

Signed-off-by: Torsten Bögershausen <redacted>
Signed-off-by: Junio C Hamano <redacted>