Fix a memory leak for the BIOCSETWF ioctl on kernels with the BPF_JITTER

option.

The BPF code was creating a compiled filter in the common filter-creation
path.  However, BPF only uses compiled filters in the read direction.
When creating a write filter, the common filter-creation code was
creating an unneeded write filter and leaking the memory used for that.

MFC after:	2 weeks
Sponsored by:	Netflix

sys/net/bpf.c

@@ -1895,8 +1895,13 @@ bpf_setf(struct bpf_d *d, struct bpf_program *fp, u_long cmd)
 			return (EINVAL);
 		}
 #ifdef BPF_JITTER
-		/* Filter is copied inside fcode and is perfectly valid. */
-		jfunc = bpf_jitter(fcode, flen);
+		if (cmd != BIOCSETWF) {
+			/*
+			 * Filter is copied inside fcode and is
+			 * perfectly valid.
+			 */
+			jfunc = bpf_jitter(fcode, flen);
+		}
 #endif
 	}