dissectors: 80211_mac_hdr: Fix clang warning

clang gives the following warning about function meas_type():

proto_80211_mac_hdr.c:1704:1: warning: control may reach end of non-void function [-Wreturn-type]
}
^

Even though this is a false positive (since we check the entire range of
an u8 in the switch/case), fix it by turning the case 13 ... 255 into
default.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
dissectors: 80211_mac_hdr: Remove remaining binary constants

Commit 151fd88f7429 ("dissectors: 80211_mac_hdr: Remove usage of binary
constants") removed binary constants in a particular case that was
reported to cause a compile error. However, this module uses binary
constants in some other places. Replace them by hexadecimal constants,
which makes it easier to read and is C99 compatible.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>