manuals: Misc macro typos

These were reported by mandoc -T lint as

ERROR: skipping unknown macro

When these pages were rendered with man, the "unknown macro" meant
that the entire line was omitted from the output.

Obvious typos in:
lib/libsys/swapon.2
lib/libsys/procctl.2
share/man/man9/firmware.9

lib/libcasper/services/cap_net/cap_net.3: 'mode' describes a function

argument.

lib/libsys/statfs.2: there's no .Tm command ("trademark?"), and

.Tn ("tradename") is deprecated, so remove the macro entirely.

usr.sbin/mfiutil/mfiutil.8: man was interpreting '/dev/' as a macro

(which it didn't recognize).

share/man/man4/qat.4: same issue as above, but with '0'. In this case,

given the context of the previous line, rewriting as "Value '0'"
seemed more appropriate.

usr.sbin/mlx5tool/mlx5tool.8: typo in .Xr

Signed-off-by: Graham Percival <gperciva@tarsnap.com>
Sponsored by: Tarsnap Backup Inc.
Reviewed by: concussious, imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/1417

(cherry picked from commit 2878d99dfcfbdd7a415a7f31cf95fbd53fc8e581)