LINUX: Reduce stack depth on recursive symlink res

LINUX: Reduce stack depth on recursive symlink res

Instead of calling vfs_follow_link inside afs_linux_follow_link
ourselves, we can just resolve the next step of the symlink resolution
and set the result in nd_set_link(), freeing the string in
.put_link().

For kernels without a usable symlink text cache, this reduces call
depth when resolving a path containing many symlinks by two frames per
layer of indirection, allowing for more deeply-nested symlink paths to
be usable.

Change-Id: I6886c3b67089c8028fd6ad93ab10eb9173bd6fbe
Reviewed-on: http://gerrit.openafs.org/3433
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Reviewed-by: Derrick Brashear <shadow@dementia.org>