rxrpc: Use umin() and umax() rather than min_t()/max_t() where possible

Use umin() and umax() rather than min_t()/max_t() where the type specified
is an unsigned type.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Link: https://patch.msgid.link/20241204074710.990092-4-dhowells@redhat.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>