docs: some manpage fixes

Some editorial changes so the man pages follow the standards.

References:
 procps#173

sysctl.8

@@ -144,7 +144,9 @@ The
 .B base_reachable_time
 and
 .B retrans_time
-are deprecated.  The sysctl command does not allow changing values of these
+are deprecated.  The
+.B sysctl
+command does not allow changing values of these
 parameters.  Users who insist to use deprecated kernel interfaces should push values
 to /proc file system by other means.  For example:
 .PP