define IPV6_CHECKSUM for freebsd and macos

Author: wg

src/unix/bsd/apple/mod.rs

@@ -2249,6 +2249,7 @@ pub const IP_PKTINFO: ::c_int = 26;
 pub const IP_RECVTOS: ::c_int = 27;
 pub const IPV6_JOIN_GROUP: ::c_int = 12;
 pub const IPV6_LEAVE_GROUP: ::c_int = 13;
+pub const IPV6_CHECKSUM: ::c_int = 26;
 pub const IPV6_RECVTCLASS: ::c_int = 35;
 pub const IPV6_TCLASS: ::c_int = 36;
 pub const IPV6_PKTINFO: ::c_int = 46;

src/unix/bsd/freebsdlike/mod.rs

@@ -757,6 +757,7 @@ pub const IP_DROP_MEMBERSHIP: ::c_int = 13;
 pub const IP_RECVIF: ::c_int = 20;
 pub const IPV6_JOIN_GROUP: ::c_int = 12;
 pub const IPV6_LEAVE_GROUP: ::c_int = 13;
+pub const IPV6_CHECKSUM: ::c_int = 26;
 pub const IPV6_RECVPKTINFO: ::c_int = 36;
 pub const IPV6_PKTINFO: ::c_int = 46;
 pub const IPV6_RECVTCLASS: ::c_int = 57;