LP#1628995 Fix output message length calculation

LP#1628995 Fix output message length calculation

In cases where an output message has a different number of logical
characters than bytes, SIPServer can incorrectly calculate the
length of the message, resulting in an incomplete message being
sent. Since the message lacks the SIP2 Message Terminator character
(CR, 0x0d), client behavior is unpredictable. Some clients will
hang.

A "use bytes;" pragma forces the length() call to disable character
semantics, so that the correct number of bytes is passed to
POSIX::write().

Future changes may result in output messages never reaching this
point in a state where Perl will apply character semantics, but for
now this handles the problem without hanging clients.

Signed-off-by: Jeff Godin <jgodin@tadl.org>