src: remove redundant casts

All of them are implicitly convertable without any wanted side effects.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/extensions/libxt_tcp.c b/extensions/libxt_tcp.c
index 14d8c18..a9039f0 100644
--- a/extensions/libxt_tcp.c
+++ b/extensions/libxt_tcp.c
@@ -124,7 +124,7 @@
 	if (string_to_number(option, 1, 255, &ret) == -1)
 		exit_error(PARAMETER_PROBLEM, "Bad TCP option `%s'", option);
 
-	*result = (u_int8_t)ret;
+	*result = ret;
 }
 
 static void tcp_init(struct xt_entry_match *m)