pppx(4): kill needless check

[Vitaliy Makkoveev]

Just quick cleanup.

Index: sys/net/if_pppx.c
===================================================================
RCS file: /cvs/src/sys/net/if_pppx.c,v
retrieving revision 1.79
diff -u -p -r1.79 if_pppx.c
--- sys/net/if_pppx.c   6 Apr 2020 12:31:30 -0000       1.79
+++ sys/net/if_pppx.c   6 Apr 2020 19:22:13 -0000
@@ -720,8 +720,6 @@ pppx_add_session(struct pppx_dev *pxd, s
        }
 
        pxi = pool_get(pppx_if_pl, PR_WAITOK | PR_ZERO);
-       if (pxi == NULL)
-               return (ENOMEM);
 
        session = &pxi->pxi_session;
        ifp = &pxi->pxi_if;