Add netinet/in.h values from Linux 4.2.

This patch adds new constants from Linux 4.2 to netinet/in.h:
IPPROTO_MPLS and IP_BIND_ADDRESS_NO_PORT (both in
include/uapi/linux/in.h in Linux; one directly in netinet/in.h, one in
bits/in.h in glibc).

Tested for x86_64 (testsuite, and that installed stripped shared
libraries are unchanged by the patch).

	* inet/netinet/in.h (IPPROTO_MPLS): New enum value and macro.
	* sysdeps/unix/sysv/linux/bits/in.h (IP_BIND_ADDRESS_NO_PORT): New
	macro.