Define IP_FREEBIND for Fuchsia

https://cs.opensource.google/fuchsia/fuchsia/+/master:zircon/third_party/ulib/musl/include/netinet/in.h;l=196;drc=bdf60afa9193c8a9190ee6bb6b5a0a11ad8876b6

Author: tamird

src/fuchsia/mod.rs

@@ -1768,14 +1768,17 @@ pub const SCM_TIMESTAMP: ::c_int = SO_TIMESTAMP;
 
 pub const SOCK_RAW: ::c_int = 3;
 pub const SOCK_RDM: ::c_int = 4;
+
+pub const IP_TTL: ::c_int = 2;
+pub const IP_HDRINCL: ::c_int = 3;
+pub const IP_FREEBIND: ::c_int = 15;
+pub const IP_TRANSPARENT: ::c_int = 19;
 pub const IP_MULTICAST_IF: ::c_int = 32;
 pub const IP_MULTICAST_TTL: ::c_int = 33;
 pub const IP_MULTICAST_LOOP: ::c_int = 34;
-pub const IP_TTL: ::c_int = 2;
-pub const IP_HDRINCL: ::c_int = 3;
 pub const IP_ADD_MEMBERSHIP: ::c_int = 35;
 pub const IP_DROP_MEMBERSHIP: ::c_int = 36;
-pub const IP_TRANSPARENT: ::c_int = 19;
+
 pub const IPV6_UNICAST_HOPS: ::c_int = 16;
 pub const IPV6_MULTICAST_IF: ::c_int = 17;
 pub const IPV6_MULTICAST_HOPS: ::c_int = 18;