ebtables: Merge OPT_* flags with xshared ones

ebtables: Merge OPT_* flags with xshared ones

Despite also including xshared.h, xtables-eb.c defined its own OPT_*
flags with clashing values. Albeit ugly, this wasn't a problem in
practice until commit 51d9d9e081344 ("ebtables: Support verbose mode")
which introduced use of OPT_VERBOSE from xshared - with same value as
the local OPT_PROTOCOL define.

Eliminate the clash by appending ebtables-specific flags to the xshared
enum and adjust for the different names of some others.

Fixes: 51d9d9e081344 ("ebtables: Support verbose mode")
Signed-off-by: Phil Sutter <phil@nwl.cc>