afs_pioctl: avoid -Wpointer-sign

afs_pioctl: avoid -Wpointer-sign

Change the declaration of 'addr' to be a signed int, to match
RXAFS_CallBackRxConnAddr() and the afsd_pd_GetInt() used with it.
This was detected by clang 4.0 in FreeBSD 11.1, via -Wpointer-sign.

Reviewed-on: https://gerrit.openafs.org/12934
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 79f33b859aeb3c91f2cce7597fdc138978c4e1d9)

Change-Id: Iee85059bebfc8d6fbda3409b720576bd4f6c5f8f
Reviewed-on: https://gerrit.openafs.org/12938
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>