libwebsockets: bump to 1.7.5

Minor fixes, see
https://github.com/warmcat/libwebsockets/blob/v1.7-stable/changelog for
full changelog.

Signed-off-by: Karl Palsson <karlp@etactica.com>

libs/libwebsockets/Makefile

@@ -8,7 +8,7 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=libwebsockets
-PKG_VERSION:=1.7.3
+PKG_VERSION:=1.7.5
 PKG_RELEASE:=1
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.xz