[v2] nsswitch: do not reload if "/" changes

[Joseph Myers]

This has broken the testsuite build for Hurd.

tst-reload2.c: In function 'do_test':
tst-reload2.c:78:13: error: 'PATH_MAX' undeclared (first use in this function)
   78 |   char buf1[PATH_MAX];
      |             ^~~~~~~~
tst-reload2.c:78:13: note: each undeclared identifier is reported only once for each function it appears in

https://sourceware.org/pipermail/libc-testresults/2021q1/007436.html

-- 
Joseph S. Myers
joseph@codesourcery.com