man: ip-token.8: Review synopsis section

Drop unnecessary curly braces around single action keywords, point out
that 'dev' parameter to 'ip token get' is optional and clarify that 'ip
token' defaults to 'list' action.
Signed-off-by: Phil Sutter <phil@nwl.cc>

man/man8/ip-token.8

@@ -7,23 +7,23 @@ ip-token \- tokenized interface identifier support
 .in +8
 .ti -8
 .B ip token
-.RI " { " COMMAND " | "
+.RI "{ " COMMAND " | "
 .BR help " }"
 .sp
 
 .ti -8
-.BR "ip token" " { " set " } "
+.B ip token set
 .IR TOKEN
 .B dev
 .IR DEV
 
 .ti -8
-.BR "ip token" " { " get " } "
-.B dev
-.IR DEV
+.B ip token get
+.RB "[ " dev
+.IR DEV " ]"
 
 .ti -8
-.BR "ip token" " { " list " }"
+.BR "ip token" " [ " list " ]"
 
 .SH "DESCRIPTION"
 IPv6 tokenized interface identifier support is used for assigning well-known