fix(config): drop the uptime line from get_config()

`show running-config` is preceded by a header block, and one of its lines
reports the system uptime. That value necessarily differs between any two
reads, so every caller comparing consecutive configs sees a change each
time.

Measured on a GS110TPv3 under NetOrk: 876 of 894 stored config snapshots
marked as changed, one git commit and one config_changed warning per poll,
while every other device at the same installation sat between 2 and 18. The
history was worthless for that switch — a genuine change would have been
invisible among hundreds of uptime diffs.

Only the uptime line is removed. Model, firmware version, serial and MAC are
stable and belong in a config backup; a changed firmware version is exactly
the kind of change worth recording.

netgear_plus is unaffected — its get_config() returns empty strings.

The first read after this lands reports one real change, since the line
disappears from the stored config. That is unavoidable and happens once.

napalm_netgear/netgear_smart.py

@@ -821,6 +821,29 @@ class NetgearSmartDriver(ConfigLifecycleMixin, SwitchDriver):
 
         return interfaces_ip
 
+    _RUNTIME_STATE_LINE = re.compile(r"^\s*!\s*System Up Time:", re.IGNORECASE)
+
+    @classmethod
+    def _strip_runtime_state(cls, config: str) -> str:
+        """Drop lines describing state rather than configuration.
+
+        ``show running-config`` is preceded by a header block, and one of its
+        lines reports the system uptime. That value necessarily differs
+        between any two reads, so a caller diffing consecutive configs sees a
+        change every single time — on a GS110TPv3 that marked 876 of 894
+        stored snapshots as changed and made the history useless.
+
+        Only the uptime line goes. The rest of the header (model, firmware,
+        serial, MAC) is stable, and a changed firmware version is precisely
+        the kind of change a config backup should record.
+        """
+        if not config:
+            return config
+        kept = [
+            ln for ln in config.splitlines(keepends=True) if not cls._RUNTIME_STATE_LINE.match(ln)
+        ]
+        return "".join(kept)
+
     def get_config(
         self,
         retrieve: str = "all",
@@ -836,10 +859,14 @@ class NetgearSmartDriver(ConfigLifecycleMixin, SwitchDriver):
         configs = {"running": "", "startup": "", "candidate": ""}
 
         if retrieve in ("all", "running"):
-            configs["running"] = self._send_paged_command("show running-config")
+            configs["running"] = self._strip_runtime_state(
+                self._send_paged_command("show running-config")
+            )
 
         if retrieve in ("all", "startup"):
-            configs["startup"] = self._send_paged_command("show startup-config")
+            configs["startup"] = self._strip_runtime_state(
+                self._send_paged_command("show startup-config")
+            )
 
         if sanitized:
             configs = napalm_helpers.sanitize_configs(configs, C.CISCO_SANITIZE_FILTERS)