unused variable i in handle_structured_reply()

[pgajdos]

nbd-server.c:2538:13: warning: unused variable ‘i’

[pgajdos]

There are also more gcc warnings, -Wunused-variable -Wdiscarded-qualifiers -Wunused-but-set-variable -Wunused-function -Waddress should be the full list.

This is JFYI, if you are fine with that, feel free to close.

[pgajdos]

(I can also try to come up with a patch upon request.)