Don't use memcpy() to write blueflame sends

Don't use memcpy() to write blueflame sends

Some memcpy() implementations may use move-string-buffer assembly
instructions, which do not guarantee copy order into the blueflame
buffer.  This causes problems when writing into a blueflame buffer, so
use our own copy function instead.

Signed-off-by: Jack Morgenstein <jackm@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>