ioshark: fix posix_fadvise error checking.

posix_ and pthread_ routines [almost all] return errno values on
failure.

Also stop reporting errno when we can give a message instead.

(This code should probably use error(3) instead, but that's a bigger
cleanup and I'm not sure this isn't all dead code anyway.)

Test: builds
Change-Id: I11e5927e4d797cd213f574fe414c021829625483
1 file changed