Use r271207 optimization only for MSI-enabled HBAs.

It was found that VirtualBox' AHCI does not allow nterrupt to be cleared
before the interrupt status register is read, causing interrupt storm.

AHCI specification allows to skip this register use when multi-vector MSI
is enabled and so interrupting port is known.  For single-vector MSI that
is not stated explicitly, but if the port is only one, it is obviously
known too.
Improve "reserved keywords" hack:

we can't easily predict (in current parsing model)
if the keyword is ipfw(8) reserved keyword or port name.
Checking proto database via getprotobyname() consumes a lot of
CPU and leads to tens of seconds for parsing large ruleset.
Use list of reserved keywords and check them as pre-requisite
before doing getprotobyname().

Obtained from:	Yandex LLC