WireGuardKit: fix incorrect IP address allocation size

According to [1], the `capacity` parameter is specified as "the number
of instances of T in the re-bound region" and not the total size of the
rebound struct.

Without this patch, there are crashes in the extension with the
following error:

  Fatal error: self must be a properly aligned pointer for types Pointee and T`

Since the subsequent line in the code only reads `sizeof(in_addr)` or
`sizeof(in6_addr)` anyway, change the `capacity` parameter to just be a
count of 1.

[1] https://developer.apple.com/documentation/swift/unsafepointer/withmemoryrebound(to:capacity:_:)

Signed-off-by: John Biggs <john.biggs@proton.ch>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

Sources/WireGuardKit/IPAddress+AddrInfo.swift

@@ -8,7 +8,7 @@ extension IPv4Address {
     init?(addrInfo: addrinfo) {
         guard addrInfo.ai_family == AF_INET else { return nil }
 
-        let addressData = addrInfo.ai_addr.withMemoryRebound(to: sockaddr_in.self, capacity: MemoryLayout<sockaddr_in>.size) { ptr -> Data in
+        let addressData = addrInfo.ai_addr.withMemoryRebound(to: sockaddr_in.self, capacity: 1) { ptr -> Data in
             return Data(bytes: &ptr.pointee.sin_addr, count: MemoryLayout<in_addr>.size)
         }
 
@@ -20,7 +20,7 @@ extension IPv6Address {
     init?(addrInfo: addrinfo) {
         guard addrInfo.ai_family == AF_INET6 else { return nil }
 
-        let addressData = addrInfo.ai_addr.withMemoryRebound(to: sockaddr_in6.self, capacity: MemoryLayout<sockaddr_in6>.size) { ptr -> Data in
+        let addressData = addrInfo.ai_addr.withMemoryRebound(to: sockaddr_in6.self, capacity: 1) { ptr -> Data in
             return Data(bytes: &ptr.pointee.sin6_addr, count: MemoryLayout<in6_addr>.size)
         }