pppx(4): kill forgotten splx(9) stuff

[Vitaliy Makkoveev]

pppx_if containing tree and per pppx_dev list are protected by rwlock so
these splx(9) related dances and commentaries are not actual.
Also pxd_svcq protected by NET_LOCK().

Index: sys/net/if_pppx.c
===================================================================
RCS file: /cvs/src/sys/net/if_pppx.c,v
retrieving revision 1.81
diff -u -p -r1.81 if_pppx.c
--- sys/net/if_pppx.c   7 Apr 2020 07:11:22 -0000       1.81
+++ sys/net/if_pppx.c   7 Apr 2020 09:06:35 -0000
@@ -126,7 +126,7 @@ struct pppx_dev {
        struct selinfo          pxd_wsel;
        struct mutex            pxd_wsel_mtx;
 
-       /* queue of packets for userland to service - protected by splnet */
+       /* queue of packets for userland to service - protected by NET_LOCK() */
        struct mbuf_queue       pxd_svcq;
        int                     pxd_waiting;
        LIST_HEAD(,pppx_if)     pxd_pxis;
@@ -622,7 +622,6 @@ pppx_if_next_unit(void)
 
        rw_assert_wrlock(&pppx_ifs_lk);
 
-       /* this is safe without splnet since we're not modifying it */
        do {
                int found = 0;
                RBT_FOREACH(pxi, pppx_ifs, &pppx_ifs) {
@@ -842,7 +841,6 @@ pppx_add_session(struct pppx_dev *pxd, s
        pxi->pxi_key.pxik_protocol = req->pr_protocol;
        pxi->pxi_dev = pxd;
 
-       /* this is safe without splnet since we're not modifying it */
        if (RBT_FIND(pppx_ifs, &pppx_ifs, pxi) != NULL) {
                pool_put(pppx_if_pl, pxi);
                error = EADDRINUSE;
@@ -850,8 +848,7 @@ pppx_add_session(struct pppx_dev *pxd, s
                goto out;
        }
 
-       if (RBT_INSERT(pppx_ifs, &pppx_ifs, pxi) != NULL)
-               panic("%s: pppx_ifs modified while lock was held", __func__);
+       RBT_INSERT(pppx_ifs, &pppx_ifs, pxi);
        LIST_INSERT_HEAD(&pxd->pxd_pxis, pxi, pxi_list);
        rw_exit_write(&pppx_ifs_lk);
 
@@ -1039,8 +1036,7 @@ pppx_if_destroy(struct pppx_dev *pxd, st
        NET_LOCK();
 
        rw_enter_write(&pppx_ifs_lk);
-       if (RBT_REMOVE(pppx_ifs, &pppx_ifs, pxi) == NULL)
-               panic("%s: pppx_ifs modified while lock was held", __func__);
+       RBT_REMOVE(pppx_ifs, &pppx_ifs, pxi);
        LIST_REMOVE(pxi, pxi_list);
        rw_exit_write(&pppx_ifs_lk);