vsftpd: fix compilation with glibc

Fix compilation for glibc by removing -lnsl flag

Reported-by: Ian Cooper <iancooper@hotmail.com>
Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>

net/vsftpd/Makefile

@@ -52,6 +52,8 @@ Package/vsftpd-tls/conffiles=$(Package/vsftpd/conffiles)
 
 ifneq ($(CONFIG_USE_MUSL),)
   NLSSTRING:=-lcrypt
+else ifneq ($(CONFIG_USE_GLIBC),)
+  NLSSTRING:=-lcrypt
 else
   NLSSTRING:=-lcrypt -lnsl
 endif