libceph: fix "Boolean result is used in bitwise operation" warning

This line dates back to 2013, but cppcheck complained because commit
2f713615

 ("libceph: move msgr1 protocol implementation to its own
file") moved it.  Add parenthesis to silence the warning.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>