lib: make IPv6 prefix parser slightly more strict

This makes it possible to have both "show babel route A.B.C.D/M"
and "show babel route X:X::X:X/M" commands at the same time without
the parser complaining about ambiguity.

* lib/command.c: only accept STATE_DOT after : was seen.

Reported-by: Juliusz Chroboczek <jch@pps.jussieu.fr>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/lib/command.c b/lib/command.c
index 4d95e92..64563b5 100644
--- a/lib/command.c
+++ b/lib/command.c
@@ -954,7 +954,12 @@
 	      if (*(str + 1) == ':')
 		state = STATE_COLON;
 	      else if (*(str + 1) == '.')
-		state = STATE_DOT;
+		{
+		  if (colons || double_colon)
+		    state = STATE_DOT;
+		  else
+		    return no_match;
+		}
 	      else if (*(str + 1) == '/')
 		state = STATE_SLASH;
 	    }