Added link MTU discovery configuration option

RNS/Link.py

@@ -245,7 +245,7 @@ class Link:
         if self.initiator:
             link_mtu = b""
             nh_hw_mtu = RNS.Transport.next_hop_interface_hw_mtu(destination.hash)
-            if RNS.Reticulum.LINK_MTU_DISCOVERY and nh_hw_mtu:
+            if RNS.Reticulum.link_mtu_discovery() and nh_hw_mtu:
                 link_mtu = Link.mtu_bytes(nh_hw_mtu)
                 RNS.log(f"Signalling link MTU of {RNS.prettysize(nh_hw_mtu)} for link", RNS.LOG_DEBUG) # TODO: Remove debug
             self.request_data = self.pub_bytes+self.sig_pub_bytes+link_mtu

RNS/Reticulum.py

@@ -235,6 +235,7 @@ class Reticulum:
         Reticulum.interfacepath = Reticulum.configdir+"/interfaces"
 
         Reticulum.__transport_enabled = False
+        Reticulum.__link_mtu_discovery = Reticulum.LINK_MTU_DISCOVERY
         Reticulum.__remote_management_enabled = False
         Reticulum.__use_implicit_proof = True
         Reticulum.__allow_probes = False
@@ -433,6 +434,10 @@ class Reticulum:
                     v = self.config["reticulum"].as_bool(option)
                     if v == True:
                         Reticulum.__transport_enabled = True
+                if option == "link_mtu_discovery":
+                    v = self.config["reticulum"].as_bool(option)
+                    if v == True:
+                        Reticulum.__link_mtu_discovery = True
                 if option == "enable_remote_management":
                     v = self.config["reticulum"].as_bool(option)
                     if v == True:
@@ -1238,6 +1243,20 @@ class Reticulum:
         """
         return Reticulum.__transport_enabled
 
+    @staticmethod
+    def link_mtu_discovery():
+        """
+        Returns whether link MTU discovery is enabled for the running
+        instance.
+
+        When link MTU discovery is enabled, Reticulum will
+        automatically upgrade link MTUs to the highest supported
+        value, increasing transfer speed and efficiency.
+
+        :returns: True if link MTU discovery is enabled, False if not.
+        """
+        return Reticulum.__link_mtu_discovery
+
     @staticmethod
     def remote_management_enabled():
         """