MDEV-15655: abstract socket support - limit length
MDEV-15655: abstract socket support - limit length

Unlike UNIX filesystem sockets, abstract sockets need to be length
limited because nulls are insignificant in the name.

Limiting this doesn't have any effect on UNIX filesystem sockets.

Thanks to Sergey Vojtovich

ottok/mariadb-connector-c,MariaDB/mariadb-connector-c,ottok/mariadb-connector-c,ottok/mariadb-connector-c,MariaDB/mariadb-connector-c,MariaDB/mariadb-connector-c