config: allow changing "skipmerklecheck" at runtime

requested by shesek for "bwt"

electrum/commands.py

@@ -1274,7 +1274,7 @@ def add_network_options(parser):
     parser.add_argument("-s", "--server", dest="server", default=None, help="set server host:port:protocol, where protocol is either t (tcp) or s (ssl)")
     parser.add_argument("-p", "--proxy", dest="proxy", default=None, help="set proxy [type:]host[:port] (or 'none' to disable proxy), where type is socks4,socks5 or http")
     parser.add_argument("--noonion", action="store_true", dest="noonion", default=None, help="do not try to connect to onion servers")
-    parser.add_argument("--skipmerklecheck", action="store_true", dest="skipmerklecheck", default=False, help="Tolerate invalid merkle proofs from server")
+    parser.add_argument("--skipmerklecheck", action="store_true", dest="skipmerklecheck", default=None, help="Tolerate invalid merkle proofs from server")
 
 def add_global_options(parser):
     group = parser.add_argument_group('global options')