Quiet compiler warnings for fget_noref and fdget_noref

[stevek]

Summary

Typecasting both parts of the comparison to u_int quiets compiler
warnings about signed/unsigned comparison and takes care of positive
and negative numbers for the file descriptor in a single comparison.

Obtained from: Juniper Netwowrks, Inc.

[mjg]

fdt_nfiles should probably become unsigned instead and whatever which does not already (u_int)fd should start doing it

what compiler are you using?

[stevek]

In D39593#901233, @mjg wrote:

fdt_nfiles should probably become unsigned instead and whatever which does not already (u_int)fd should start doing it

what compiler are you using?

Using clang. I believe it was caught by the -Wsign-compare warning.