control/controlclient: free memory on iOS before full netmap work

Updates tailscale/corp#18514

Change-Id: I8d0330334b030ed8692b25549a0ee887ac6d7188
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f