if uClibc_config.h doesnt exist yet, make sure grep doesnt complain about it

package/ipsec-tools/ipsec-tools.mk

@@ -42,7 +42,7 @@ IPSEC_TOOLS_CONFIG_FLAGS+=	--disable-stats
 endif
 
 # At first check, if uClibc supports IPv6
-ifeq ($(shell grep -q '__UCLIBC_HAS_IPV6__ 1' \
+ifeq ($(shell grep -qs '__UCLIBC_HAS_IPV6__ 1' \
 	$(STAGING_DIR)/include/bits/uClibc_config.h && echo IPV6), IPV6)
 
 ifeq ($(strip $(BR2_PACKAGE_IPSEC_TOOLS_IPV6)), y)