When using control masters also enable keep alives

Prevents the master connection from becoming stale. Use ssh protocol
keep alives rather than tcp ones as tcp ones are often blocked by
firewalls and also spoofable.

kittens/ssh/main.py

@@ -447,6 +447,9 @@ def connection_sharing_args(opts: SSHOptions, kitty_pid: int) -> List[str]:
         '-o', 'ControlMaster=auto',
         '-o', f'ControlPath={cp}',
         '-o', 'ControlPersist=yes',
+        '-o', 'ServerAliveInterval=60',
+        '-o', 'ServerAliveCountMax=5',
+        '-o', 'TCPKeepAlive=no',
     ]
     return ans