SUNRPC: use assign_bit() where applicable

Convert open-coded if/else with set_bit/clear_bit the assign_bit API.

Done with Coccinelle semantic patch:
    // set_bit -> clear_bit => assign_bit

    @@
    expression cond, bit, addr;
    @@

    -if (cond)
    -        set_bit(bit, addr);
    -else
    -        clear_bit(bit, addr);
    +assign_bit(bit, addr, cond);

    @@
    expression cond, bit, addr;
    @@

    -if (cond)
    -        clear_bit(bit, addr);
    -else
    -        set_bit(bit, addr);
    +assign_bit(bit, addr, !cond);

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Link: https://patch.msgid.link/20260920022714.3145751-1-peng.fan@oss.nxp.com
Signed-off-by: Chuck Lever <cel@kernel.org>