Ip: allow set_mtu to skip asserting the resulting mtu

Some drivers silently clamp or ignore an mtu change, and callers that
only want a best effort change had no way to avoid the assertion. Add
assert_success, defaulting to the existing behavior, and log the
mismatch instead of failing when it is disabled.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 5d5f58ad-b9df-4420-ad37-22caee78e925

Author: mcgov

lisa/tools/ip.py

@@ -257,15 +257,22 @@ def get_mtu(self, nic_name: str) -> int:
         cat = self.node.tools[Cat]
         return int(cat.read(f"/sys/class/net/{nic_name}/mtu", force_run=True))
 
-    def set_mtu(self, nic_name: str, mtu: int) -> None:
+    def set_mtu(self, nic_name: str, mtu: int, assert_success: bool = True) -> None:
         # Check if mtu is integer
         try:
             mtu = int(mtu)
         except ValueError:
             raise LisaException(f"MTU value is not an integer: {mtu}")
         self.run(f"link set dev {nic_name} mtu {mtu}", force_run=True, sudo=True)
+        
         new_mtu = self.get_mtu(nic_name=nic_name)
-        assert_that(new_mtu).described_as("set mtu failed").is_equal_to(mtu)
+        if new_mtu != mtu:
+            if assert_success:
+                raise LisaException(f"set mtu failed, wanted {mtu} and got {new_mtu}")
+            else:
+                self.node.log.debug(
+                    "set_mtu: skipping result assertion since assert_success was False. "
+                )
 
     def nic_exists(self, nic_name: str) -> bool:
         result = self.run(f"link show {nic_name}", force_run=True, sudo=True)