nixos-rebuild: set SSHOPTS earlier so that we resolve the correct hostname (#354283)

pkgs/os-specific/linux/nixos-rebuild/nixos-rebuild.sh

@@ -427,6 +427,25 @@ if [[ -z $flake && -e /etc/nixos/flake.nix && -z $noFlake ]]; then
     flake="$(dirname "$(readlink -f /etc/nixos/flake.nix)")"
 fi
 
+tmpDir=$(mktemp -t -d nixos-rebuild.XXXXXX)
+
+if [[ ${#tmpDir} -ge 60 ]]; then
+    # Very long tmp dirs lead to "too long for Unix domain socket"
+    # SSH ControlPath errors. Especially macOS sets long TMPDIR paths.
+    rmdir "$tmpDir"
+    tmpDir=$(TMPDIR= mktemp -t -d nixos-rebuild.XXXXXX)
+fi
+
+cleanup() {
+    for ctrl in "$tmpDir"/ssh-*; do
+        ssh -o ControlPath="$ctrl" -O exit dummyhost 2>/dev/null || true
+    done
+    rm -rf "$tmpDir"
+}
+trap cleanup EXIT
+
+SSHOPTS="$NIX_SSHOPTS -o ControlMaster=auto -o ControlPath=$tmpDir/ssh-%n -o ControlPersist=60"
+
 # For convenience, use the hostname as the default configuration to
 # build from the flake.
 if [[ -n $flake ]]; then
@@ -450,23 +469,6 @@ if [[ ! -z "$specialisation" && ! "$action" = switch && ! "$action" = test ]]; t
     exit 1
 fi
 
-tmpDir=$(mktemp -t -d nixos-rebuild.XXXXXX)
-
-if [[ ${#tmpDir} -ge 60 ]]; then
-    # Very long tmp dirs lead to "too long for Unix domain socket"
-    # SSH ControlPath errors. Especially macOS sets long TMPDIR paths.
-    rmdir "$tmpDir"
-    tmpDir=$(TMPDIR= mktemp -t -d nixos-rebuild.XXXXXX)
-fi
-
-cleanup() {
-    for ctrl in "$tmpDir"/ssh-*; do
-        ssh -o ControlPath="$ctrl" -O exit dummyhost 2>/dev/null || true
-    done
-    rm -rf "$tmpDir"
-}
-trap cleanup EXIT
-
 
 # Re-execute nixos-rebuild from the Nixpkgs tree.
 if [[ -z $_NIXOS_REBUILD_REEXEC && -n $canRun && -z $fast ]]; then
@@ -510,8 +512,6 @@ if [ "$action" = edit ]; then
     exit 1
 fi
 
-SSHOPTS="$NIX_SSHOPTS -o ControlMaster=auto -o ControlPath=$tmpDir/ssh-%n -o ControlPersist=60"
-
 # First build Nix, since NixOS may require a newer version than the
 # current one.
 if [[ -n "$rollback" || "$action" = dry-build ]]; then