Exclude symbol of mainloop/socket from common lib

Exclude symbol of mainloop/socket from common lib

Mainloop class and Socket class is used only as private member in other
classes in common lib so it could be hidden symbol.

Change-Id: Id32237cb00a9115fc84d95294e1846e3ddc341da
Signed-off-by: Kyungwook Tak <k.tak@samsung.com>