qtconnectivity: fails to build for big endian platforms (error: 'bswap_16' was not declared in this scope)

Building qtconnectivity fails for big endian platforms because the
bswap_16 function is not declared. This is the error message:

In file included from bluez/hcimanager_p.h:52:0,
from bluez/hcimanager.cpp:35:
./bluez/bluez_data_p.h: In function 'quint16 bt_get_le16(const void*)':
./bluez/bluez_data_p.h:172:60: error: 'bswap_16' was not declared in
this scope
return bswap_16(bt_get_unaligned((const quint16 *) ptr));

bswap_16 is defined in byteswap.h so we can include this file in order
to fix this problem.