[slave.mk] use curl instead of wget (sonic-net#3939)

wget creates empty file on failure which makes subsequent make runs
think that file is already there and won't try to download it again.

e.g.:

$ make target/files/stretch/fw-SPC-rel-13_2000_2602-EVB.mfa
...
Fails to download
...
$ ls target/files/stretch/fw-SPC-rel-13_2000_2602-EVB.mfa
target/files/stretch/fw-SPC-rel-13_2000_2602-EVB.mfa
$ make target/files/stretch/fw-SPC-rel-13_2000_2602-EVB.mfa
make: `target/files/stretch/fw-SPC-rel-13_2000_2602-EVB.mfa' is up to
date.

Signed-off-by: Stepan Blyschak <stepanb@mellanox.com>

slave.mk

@@ -256,7 +256,7 @@ SONIC_TARGET_LIST += $(addprefix $(FILES_PATH)/, $(SONIC_COPY_FILES))
 $(addprefix $(DEBS_PATH)/, $(SONIC_ONLINE_DEBS)) : $(DEBS_PATH)/% : .platform
 	$(HEADER)
 	$(foreach deb,$* $($*_DERIVED_DEBS), \
-	    { wget --no-use-server-timestamps -O $(DEBS_PATH)/$(deb) $($(deb)_URL) $(LOG) || exit 1 ; } ; )
+	    { curl -f -o $(DEBS_PATH)/$(deb) $($(deb)_URL) $(LOG) || { exit 1 ; } } ; )
 	$(FOOTER)
 
 SONIC_TARGET_LIST += $(addprefix $(DEBS_PATH)/, $(SONIC_ONLINE_DEBS))
@@ -269,7 +269,7 @@ SONIC_TARGET_LIST += $(addprefix $(DEBS_PATH)/, $(SONIC_ONLINE_DEBS))
 #     SONIC_ONLINE_FILES += $(SOME_NEW_FILE)
 $(addprefix $(FILES_PATH)/, $(SONIC_ONLINE_FILES)) : $(FILES_PATH)/% : .platform
 	$(HEADER)
-	wget --no-use-server-timestamps -O  $@ $($*_URL) $(LOG)
+	curl -f -o $@ $($*_URL) $(LOG)
 	$(FOOTER)
 
 SONIC_TARGET_LIST += $(addprefix $(FILES_PATH)/, $(SONIC_ONLINE_FILES))
@@ -631,7 +631,7 @@ $(addprefix $(TARGET_PATH)/, $(SONIC_INSTALLERS)) : $(TARGET_PATH)/% : \
 	# Pass initramfs and linux kernel explicitly. They are used for all platforms
 	export debs_path="$(STRETCH_DEBS_PATH)"
 	export files_path="$(FILES_PATH)"
-	export python_debs_path="$(PYTHON_DEBS_PATH)" 
+	export python_debs_path="$(PYTHON_DEBS_PATH)"
 	export initramfs_tools="$(STRETCH_DEBS_PATH)/$(INITRAMFS_TOOLS)"
 	export linux_kernel="$(STRETCH_DEBS_PATH)/$(LINUX_KERNEL)"
 	export onie_recovery_image="$(FILES_PATH)/$(ONIE_RECOVERY_IMAGE)"