Add missing mux

src/TinyGsmClientBG96.h

@@ -552,7 +552,7 @@ protected:
     }
     waitResponse();
     DBG("### READ:", len, "from", mux);
-    sockets[mux]->sock_available = modemGetAvailable();
+    sockets[mux]->sock_available = modemGetAvailable(mux);
     return len;
   }
 

src/TinyGsmClientSaraR4.h

@@ -613,7 +613,7 @@ protected:
     streamSkipUntil('\"');
     waitResponse();
     DBG("### READ:", len, "from", mux);
-    sockets[mux]->sock_available = modemGetAvailable();
+    sockets[mux]->sock_available = modemGetAvailable(mux);
     return len;
   }
 

src/TinyGsmClientUBLOX.h

@@ -601,7 +601,7 @@ protected:
     streamSkipUntil('\"');
     waitResponse();
     DBG("### READ:", len, "from", mux);
-    sockets[mux]->sock_available = modemGetAvailable();
+    sockets[mux]->sock_available = modemGetAvailable(mux);
     return len;
   }