ebtables: Fix for broken chain renaming

ebtables: Fix for broken chain renaming

Loading extensions pollutes 'errno' value, hence before using it to
indicate failure it should be sanitized. This was done by the called
function before the parsing/netlink split and not migrated by accident.
Move it into calling code to clarify the connection.

Fixes: a7f1e208cdf9c ("nft: split parsing from netlink commands")
Signed-off-by: Phil Sutter <phil@nwl.cc>