Add new socket options for cygwin

(backport <#4350>)
(cherry picked from commit 29d3d14)

Author: Berrysoft

src/unix/cygwin/mod.rs

@@ -974,6 +974,8 @@ pub const SOL_UDP: c_int = 17;
 pub const IPTOS_LOWDELAY: u8 = 0x10;
 pub const IPTOS_THROUGHPUT: u8 = 0x08;
 pub const IPTOS_RELIABILITY: u8 = 0x04;
+pub const IPTOS_LOWCOST: u8 = 0x02;
+pub const IPTOS_MINCOST: u8 = IPTOS_LOWCOST;
 pub const IP_DEFAULT_MULTICAST_TTL: c_int = 1;
 pub const IP_DEFAULT_MULTICAST_LOOP: c_int = 1;
 pub const IP_OPTIONS: c_int = 1;
@@ -990,8 +992,18 @@ pub const IP_DROP_SOURCE_MEMBERSHIP: c_int = 16;
 pub const IP_BLOCK_SOURCE: c_int = 17;
 pub const IP_UNBLOCK_SOURCE: c_int = 18;
 pub const IP_PKTINFO: c_int = 19;
+pub const IP_RECVTTL: c_int = 21;
 pub const IP_UNICAST_IF: c_int = 31;
+pub const IP_RECVTOS: c_int = 40;
+pub const IP_MTU_DISCOVER: c_int = 71;
+pub const IP_MTU: c_int = 73;
+pub const IP_RECVERR: c_int = 75;
+pub const IP_PMTUDISC_WANT: c_int = 0;
+pub const IP_PMTUDISC_DO: c_int = 1;
+pub const IP_PMTUDISC_DONT: c_int = 2;
+pub const IP_PMTUDISC_PROBE: c_int = 3;
 pub const IPV6_HOPOPTS: c_int = 1;
+pub const IPV6_HDRINCL: c_int = 2;
 pub const IPV6_UNICAST_HOPS: c_int = 4;
 pub const IPV6_MULTICAST_IF: c_int = 9;
 pub const IPV6_MULTICAST_HOPS: c_int = 10;
@@ -1010,6 +1022,13 @@ pub const IPV6_RTHDR: c_int = 32;
 pub const IPV6_RECVRTHDR: c_int = 38;
 pub const IPV6_TCLASS: c_int = 39;
 pub const IPV6_RECVTCLASS: c_int = 40;
+pub const IPV6_MTU_DISCOVER: c_int = 71;
+pub const IPV6_MTU: c_int = 72;
+pub const IPV6_RECVERR: c_int = 75;
+pub const IPV6_PMTUDISC_WANT: c_int = 0;
+pub const IPV6_PMTUDISC_DO: c_int = 1;
+pub const IPV6_PMTUDISC_DONT: c_int = 2;
+pub const IPV6_PMTUDISC_PROBE: c_int = 3;
 pub const MCAST_JOIN_GROUP: c_int = 41;
 pub const MCAST_LEAVE_GROUP: c_int = 42;
 pub const MCAST_BLOCK_SOURCE: c_int = 43;