r26: Modified write() to be send().

r26: Modified write() to be send().
Rationale: when #define'ing _LARGEFILE_SOURCE, and _FILE_OFFSET_BITS
to 64 so as to get Large File Support, some file-related syscalls are
modified to their 64 bit counterparts; write() is one of them. And
there's no such thing as a 'large' socket, which has caused nbd-server
to hang in the write() call. Changing the write() to a send() fixed
this (and I hate ugly bugs. This one took me, like, three days ;-)