Cast Android constants used by Channel differently

Motivation:

An upcoming pull, swiftlang/swift#35707, moves Android to the same single-header
modulemap for Bionic as used on linux, but that doesn't work unless this casting
is changed. This approach works both with the current release toolchain and
with that new modulemap.

Modifications:

Change how these constants are cast.

Result:

This repo compiles for Android and the tests pass with both modulemap approaches.

Sources/NIOCore/BSDSocketAPI.swift

@@ -67,16 +67,16 @@ private let sysInet_ntop: @convention(c) (CInt, UnsafeRawPointer?, UnsafeMutable
 private let sysInet_pton: @convention(c) (CInt, UnsafePointer<CChar>?, UnsafeMutableRawPointer?) -> CInt = inet_pton
 #endif
 
-// Work around SO_TIMESTAMP/SO_RCVTIMEO being awkwardly defined in glibc.
 #if os(Android)
-let IFF_BROADCAST: CUnsignedInt = numericCast(CNIOLinux.IFF_BROADCAST.rawValue)
-let IFF_POINTOPOINT: CUnsignedInt = numericCast(CNIOLinux.IFF_POINTOPOINT.rawValue)
-let IFF_MULTICAST: CUnsignedInt = numericCast(CNIOLinux.IFF_MULTICAST.rawValue)
+let IFF_BROADCAST: CUnsignedInt = numericCast(IFF_BROADCAST)
+let IFF_POINTOPOINT: CUnsignedInt = numericCast(IFF_POINTOPOINT)
+let IFF_MULTICAST: CUnsignedInt = numericCast(IFF_MULTICAST)
 #if arch(arm)
 let SO_RCVTIMEO = SO_RCVTIMEO_OLD
 let SO_TIMESTAMP = SO_TIMESTAMP_OLD
 #endif
 #elseif os(Linux)
+// Work around SO_TIMESTAMP/SO_RCVTIMEO being awkwardly defined in glibc.
 let SO_TIMESTAMP = CNIOLinux_SO_TIMESTAMP
 let SO_RCVTIMEO = CNIOLinux_SO_RCVTIMEO
 #endif

Sources/NIOPosix/System.swift

@@ -36,9 +36,9 @@ let badOS = { fatalError("unsupported OS") }()
 
 #if os(Android)
 let INADDR_ANY = UInt32(0) // #define INADDR_ANY ((unsigned long int) 0x00000000)
-let IFF_BROADCAST: CUnsignedInt = numericCast(CNIOLinux.IFF_BROADCAST.rawValue)
-let IFF_POINTOPOINT: CUnsignedInt = numericCast(CNIOLinux.IFF_POINTOPOINT.rawValue)
-let IFF_MULTICAST: CUnsignedInt = numericCast(CNIOLinux.IFF_MULTICAST.rawValue)
+let IFF_BROADCAST: CUnsignedInt = numericCast(IFF_BROADCAST)
+let IFF_POINTOPOINT: CUnsignedInt = numericCast(IFF_POINTOPOINT)
+let IFF_MULTICAST: CUnsignedInt = numericCast(IFF_MULTICAST)
 internal typealias in_port_t = UInt16
 extension ipv6_mreq { // http://lkml.iu.edu/hypermail/linux/kernel/0106.1/0080.html
     init (ipv6mr_multiaddr: in6_addr, ipv6mr_interface: UInt32) {