rc.d/fsck: allow additional options for fsck_y_enable via fsck_y_flags

Primary intention is to allow to pass -C option to avoid (re-)checking
clean filesystems when preening fails and fsck -y kicks in.

Submitted by:	marck
Reviewed by:	current@
Approved by:	jhb (mentor)
MFC after:	1 week

etc/defaults/rc.conf

@@ -83,6 +83,7 @@ geli_swap_flags="-e aes -l 256 -s 4096 -d"	# Options for GELI-encrypted
 
 root_rw_mount="YES"	# Set to NO to inhibit remounting root read-write.
 fsck_y_enable="NO"	# Set to YES to do fsck -y if the initial preen fails.
+fsck_y_flags=""		# Additional flags for fsck -y
 background_fsck="YES"	# Attempt to run fsck in the background where possible.
 background_fsck_delay="60" # Time to wait (seconds) before starting the fsck.
 netfs_types="nfs:NFS nfs4:NFS4 smbfs:SMB portalfs:PORTAL nwfs:NWFS" # Net filesystems.

etc/rc.d/fsck

@@ -44,8 +44,8 @@ fsck_start()
 			;;
 		8)
 			if checkyesno fsck_y_enable; then
-				echo "File system preen failed, trying fsck -y."
-				fsck -y
+				echo "File system preen failed, trying fsck -y ${fsck_y_flags}"
+				fsck -y ${fsck_y_flags}
 				case $? in
 				0)
 					;;