Optimize dissect_eth_common(): cache result of get_ether_name()
In Anders profile output[1] is looks like that get_ether_name() is called
four times, twice for src and dst. get_ether_name() takes ~2% of Ir, so
caching result should reduce Ir count by 1%.
Similar thing was already done for UDP and TCP -
5235dc6ca0d7ec4e6c1fe38cae34763366830629
[1] http://www.wireshark.org/lists/wireshark-dev/201405/msg00063.html
Change-Id: I9ca582b0522387dbfaad866a48a0934693a2849f
Reviewed-on: https://code.wireshark.org/review/1808
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>
Reviewed-by: Evan Huus <eapache@gmail.com>