Sprinkle rx_GetConnection() for concision

Sprinkle rx_GetConnection() for concision

Instead of inlining the body (taking the lock, incrementing the
refcount, and dropping the lock), use the convenience function
designed for this purpose.

Reviewed-on: https://gerrit.openafs.org/12772
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 2ae84bf053fe66b73a2c77b5d71305bae2c17587)

Change-Id: I60794d877a76fbb7c8ba59207e710a20641cc8f1
Reviewed-on: https://gerrit.openafs.org/12778
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>