Add Solaris constants needed by net2
Add Solaris constants needed by net2

The added constants are
IPV6_UNICAST_HOPS,
IPV6_MULTICAST_IF,
IPV6_MULTICAST_HOPS,
IP_MULTICAST_IF.

rust-lang/libc,rust-lang-nursery/libc,rust-lang/libc,rust-lang-nursery/libc,rust-lang/libc,rust-lang-nursery/libc