net/sunrpc: Convert (void)snprintf to snprintf

(Applies on top of "Remove uses of NIPQUAD, use %pI4")

Casts to void of snprintf are most uncommon in kernel source.
9 use casts, 1301 do not.

Remove the remaining uses in net/sunrpc/

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>