ebtables: Use xtables_exit_err()

ebtables: Use xtables_exit_err()

When e.g. ebtables-nft detects an incompatible table, a stray '.' was
printed as last line of output:

| # ebtables-nft -L
| table `filter' is incompatible, use 'nft' tool.
| .

This comes from ebtables' own exit_err callback. Instead use the common
one which also provides useful version information.

While being at it, align the final error message in xtables_eb_main()
with how the others print it.

Signed-off-by: Phil Sutter <phil@nwl.cc>