httpd: refuse a configuration with a line the replay cannot take

The replay takes a line of at most 126 bytes, so a longer one is skipped
on boot. Neither the upload path nor the editor looked at line length,
so the file the user saved was not the configuration the switch would
come up with.

Reject such a body in config_take(), before the sector is erased, which
the upload path already maps to 400. The editor points at the offending
line and its length, and measures it in bytes rather than characters, so
a name written in a non-ASCII script is counted the way the switch
counts it.

CHANGELOG.md

@@ -14,6 +14,12 @@
 
 ## Fixed
 
+- Config
+  - A startup configuration line longer than the command buffer no longer stops the replay:
+    the offending line is skipped and the following lines are still applied.
+  - The web UI and the configuration upload now refuse a line the replay cannot take,
+    instead of writing it to flash.
+
 ## Breaking changes
 
 - Config