vsock/tsi: converts BSD sockaddr to Linux wire format to prevent invalid sa_family in guests

[ihexon]

BSD and Linux have different sockaddr_in layouts:

// LINUX-style
struct sockaddr_in {
    sa_family_t     sin_family;
    in_port_t       sin_port;
    struct in_addr  sin_addr;
};
// BSD-style
struct sockaddr_in {
    uint8_t	sin_len;
    sa_family_t	sin_family;
    in_port_t	sin_port;
    struct	in_addr sin_addr;
    char	sin_zero[8];
};

Without converting to LINUX-style, the sa_len field present in macOS(BSD-style) sockaddr is misinterpreted as part of sa_family by the guest kernel, causing accept() to return an invalid address family.

This crashes any guest program that inspects the peer address after accept():

$ strace /.bin/dropbearmulti dropbear -D /run/dropbear -p 2222 -r /run/dropbear/private.key -F -s -P /run/dropbear/dropbear.pid  

crash log (sa_family=0x210 which is invalid length):

  accept(3, {sa_family=0x210 /* AF_??? */, sa_data="\370\352\177\0\0\1\0\0\0\0\0\0\0\0"}, [128 => 16]) = 6                                                                                                                                                                                                             
  getpid()                                = 270                                                                                                                                                                                                                                                                        
  writev(2, [{iov_base="[270] Feb 11 03:42:36 ", iov_len=22}, {iov_base="Early exit: Failed lookup: Unrec"..., iov_len=72}], 2[270] Feb 11 03:42:36 Early exit: Failed lookup: Unrecognized address family or invalid length) = 94                                                                                     
  writev(2, [{iov_base="\n", iov_len=1}, {iov_base=NULL, iov_len=0}], 2                                                                                                                                                                                                                                                
  ) = 1                                                                                                                                                                                                                                                                                                                
  exit_group(1)                           = ?                                                                                                                                                                                                                                                                          
  +++ exited with 1 +++                           

This PR converts BSD sockaddr to Linux wire format to fix this issue

[mtjhrc]

Good work, this actually fixes the test tsi-tcp-guest-listen on macOS (tests enabled in #524 ) Thanks!

The code is a bit messy, but the whole packet.rs file and TSI protocol is - we should probably manage the structs more explicitly.