libmultipath: resolve hash collisions in pgcmp()

libmultipath: resolve hash collisions in pgcmp()

pgcmp() is using a simple xor algorithm for hashing. Main intention
here is to have a quick comparison if two paths are identical.
However, this algorithm is prone to hash collisions, so even if
two hashes match we should still check the individual paths to
avoid collisions.

Signed-off-by: Hannes Reinecke <hare@suse.de>