HBSD: try to fix panic under heavy load

 (kgdb) bt
 #0  doadump (textdump=0) at pcpu.h:219
 #1  0xffffffff803575be in db_dump (dummy=<value optimized out>, dummy2=0, dummy3=0, dummy4=0x0) at /usr/src/sys/ddb/db_command.c:533
 #2  0xffffffff8035709d in db_command (cmd_table=0x0) at /usr/src/sys/ddb/db_command.c:440
 #3  0xffffffff80356e14 in db_command_loop () at /usr/src/sys/ddb/db_command.c:493
 #4  0xffffffff80359920 in db_trap (type=<value optimized out>, code=0) at /usr/src/sys/ddb/db_main.c:251
 #5  0xffffffff80a0ffb1 in kdb_trap (type=12, code=0, tf=<value optimized out>) at /usr/src/sys/kern/subr_kdb.c:654
 #6  0xffffffff80e27b3c in trap_fatal (frame=0xfffffe085d6724a0, eva=<value optimized out>) at /usr/src/sys/amd64/amd64/trap.c:861
 #7  0xffffffff80e27ecc in trap_pfault (frame=0xfffffe085d6724a0, usermode=<value optimized out>) at /usr/src/sys/amd64/amd64/trap.c:677
 #8  0xffffffff80e274ee in trap (frame=0xfffffe085d6724a0) at /usr/src/sys/amd64/amd64/trap.c:426
 #9  0xffffffff80e097b2 in calltrap () at /usr/src/sys/amd64/amd64/exception.S:235
 #10 0xffffffff809b4af1 in __mtx_lock_sleep (c=0xffffffff817c9930, tid=18446735278713196544, opts=0, file=0x0, line=0) at /usr/src/sys/kern/kern_mutex.c:429
 #11 0xffffffff80c88812 in swap_reserve_by_cred (incr=20480, cred=<value optimized out>) at /usr/src/sys/vm/swap_pager.c:209
 #12 0xffffffff80c9e64b in vm_map_insert (map=0xfffff80041d27a28, object=0xfffff801f55cf000, offset=339968, start=42813591552, end=42813612032, prot=3 '\003', cow=10) at /usr/src/sys/vm/vm_map.c:1200
 #13 0xffffffff80c9f435 in vm_map_fixed (map=<value optimized out>, object=<value optimized out>, offset=<value optimized out>, start=<value optimized out>, length=<value optimized out>, prot=<value optimized out>, max=<value optimized out>, cow=<value optimized out>)
     at /usr/src/sys/vm/vm_map.c:1424
 #14 0xffffffff80ca4b0e in vm_mmap (map=0xfffff80041d27a28, addr=0xfffffe085d672948, size=20480, prot=0 '\0', maxprot=7 '\a', flags=262162, handle_type=<value optimized out>, handle=<value optimized out>, foff=339968) at /usr/src/sys/vm/vm_mmap.c:1678
 #15 0xffffffff80ca3ecc in sys_mmap (td=0xfffff800415dd000, uap=<value optimized out>) at /usr/src/sys/vm/vm_mmap.c:456
 #16 0xffffffff80e285dd in amd64_syscall (td=0xfffff800415dd000, traced=0) at subr_syscall.c:133
 #17 0xffffffff80e09a9b in Xfast_syscall () at /usr/src/sys/amd64/amd64/exception.S:395

 Frame 15, sys/vm/vm_mmap.c:456 is the line right after our pax_aslr_mmap call.

` uname -a` is: FreeBSD hbsd-dev-local 11.0-CURRENT FreeBSD 11.0-CURRENT #9 27a2fa4(hardened/current/master)-dirty: Fri Dec 19 11:10:01 EST 2014     shawn@hbsd-dev-local:/usr/obj/usr/src/sys/LATT-SEC  amd64

Reported-by: Shawn
Signed-off-by: Oliver Pinter <oliver.pinter@hardenedbsd.org>
(cherry picked from commit a520a380353ee0edf74b79f0d465ea1a367deade)

HBSD: fix typo, the stop should be end

Signed-off-by: Oliver Pinter <oliver.pntr@gmail.com>
(cherry picked from commit 183e42fe813da67cd05d14927b5089869f30bde4)