LDIF.pm: fix next outside loop in _write_one_entry

Fix omission from  b5addc3 and convert a "next" outside a loop into a "return".

Thanks for Jim Toth <jjtoth@vcu.edu> for reporting the bug.
RT#96203: LDAP.pm: use correct length for syswrite

Use correct length of bytes to write with syswrite() instead of default 15000
in _sendmesg().

According to the bug reporter, it may cause error in case that the function
WRITE was redefined (e.g. Authen-SASL RT#85294) and did not handle this case
properly.

It should not change anything in Net::LDAP but help other modules not covering
all WRITE cases.
LDAP.pm: set SSL_cipher_list to correct value

Fix commit 11fe2a9 which contains a superfluous defined and thus
set SSL_cipher_list to true instead of the value of the ciphers arg.

Thanks to THOMAS GUEVIN <THOMAS.GUEVIN@adtran.com> for reporting the bug.