quota: allow usage of getrpcbynumber() instead of getrpcbynumber_r()

libtirpc does not implement the reentrant function getrpcbynumber_r(),
so allow quota to use the non-reentrant version getrpcbynumber(). This
should not be a problem as quota tools are not multi-threaded.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>