net/smc: use helper smc_conn_abort() in listen processing

The helper smc_connect_abort() can be used by the listen processing
functions, too. And rename this helper to smc_conn_abort() to make the
purpose clearer.
No functional change.

Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>